Develop Reference

The phone return empty when I want to get the phone number

Some phones return null when I want to get the phone number. In other phones I get the phone number.
This happens when Settings -> About Phone -> Status -> My phone number is "Unkow". Not writed there the phone number.
Why is this happening?How can I get a phone number ?
The code:
<uses-permission android:name="android.permission.READ_PHONE_STATE"/>
And:
TelephonyManager tMgr = (TelephonyManager)getApplicationContext().getSystemService(Context.TELEPHONY_SERVICE);
String mPhoneNumber = tMgr.getLine1Number();

Your code is perfect to get phone number of Android device.It will return you number.But sometimes it gives you null because that devices Service provider has not given permission to do that.
Means It works like : Android devices Request SIM card/Service provider for card info with phone number. And In response, Some provider have returned phone number of user and some has refused to do so.

Can you clarify what specifically you're asking for? If you're saying that it happens when in your phone's settings, under About Phone->Status->My phone number, it says "Unknown", then unfortunately that's not a programming question and not a question for here. Is that the case?

You cannot get device phone number in any ways. It depends on the service provider, some may allow access and some may not since it is completely dependent on the network access privileges. But in rare case you would get the phone number once the user has configured their own mobile number with the SIM card provider. The other way to do this by fetching the number from Facebook that too the user should have registered their mobile number, whereas the earlier versions of whatsapp provides this feature, but it is not compatible with the newer ones.
Note: It works with few custom phones which provides the access.(i.e., phones synced with only particular network providers)

Perfect unique_id for device except IMEI,Android_ID,WLAN Mac and Bluetooth address

Objective:
I am looking for a way to find out a unique_id for android device.
Background:
I will use the Id in login request payload and as my app is license based service app the Id should not change under normal circumstances.
Existing Approaches:
In iOS there are some unique id solutions for iOS such as CFUUID or identifierForVendor coupled with Keychain,Advertising Identifier etc.. that can do this job upto the expectation.
But in Android all the options that I know seems to have hole in it.
IMEI:
TelephonyManager TelephonyMgr = (TelephonyManager)getSystemService(TELEPHONY_SERVICE);
String m_deviceId = TelephonyMgr.getDeviceId();
Drawbacks
It is sim card dependent so
If there is no sim card then we're doomed
If there is dual sim then we're dommed
Android_ID:
String m_androidId = Secure.getString(getContentResolver(), Secure.ANDROID_ID);
Drawbacks
If OS version is upgraded then it may change
If device is rooted it gets changed
No guarantee that the device_id is unique there are some reports some manufacturers are having duplicate device_id
The WLAN MAC Address
WifiManager m_wm = (WifiManager)getSystemService(Context.WIFI_SERVICE);
String m_wlanMacAdd = m_wm.getConnectionInfo().getMacAddress();
Drawbacks
If there is no wifi hardware then we're doomed
In some new devices If wifi is off then we're doomed.
Bluetooth Address:
BluetoothAdapter m_BluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
String m_bluetoothAdd = m_BluetoothAdapter.getAddress();
Drawbacks:
if there is no bluetooth hardware we're doomed.
In future in some new devices we mightn't able to read it if its off.
Possible solutions:
There are two approaches that I think to solve this problem
We generate a random id by hashing timestamp with unique ids that I have mentioned and store it so next time during login we’ll check if the the stored value of key is null if its so then we’ll generate and store it else we’ll use the value of the key.
If there is something equivalent to keychain of iOS then we’re good with this approach.
Find a global identifier something like advertisingIdentifier of iOS which is same for all the apps in the device.
Any help is appreciated !

I have chosen to use Android_ID since It's not dependent on any hardware.
Build.SERIAL also dependent on availability of telephony that is in wifi only devices this Build.SERIAL won't work.
I have explained how other approaches are dependent upon the hardware availability in the question itself.

There is no such ID available on Android. You can generate your own, for example a random UUID and connect it to the user's account. This is what Kindle, Audible and other applications do to identify devices in a non-privacy-intrusive way.
Consider Google Analytics Mobile if you want to "track your users", http://www.google.com/analytics/mobile/
If you want to get closer to tracking a device you can combine the IDs above together in a hash-function. Bluetooth + wifi + android serial, and if any of them are null, you put a 0 in the hash, e.g. if there is no wifi mac addr. As you point out, you aren't guaranteed the id won't change. Unless the user is running a custom ROM, I would expect this computed ID to stay constant, though.

I think, you could use device serial ID (hardware serial number, not android id). You could seen it in device settings. In your code, you could get it by Build.SERIAL.

Restrict android application to specific region

I want my application to work in specific region e.g US.
We can limit distribution of application from play market but i found there are some hacks to install those apps.
I have to somehow limit the use within application.
For that I can retrieve user's GPS location and use Google's Geocode API for first run. But what if user travels to some other region?
I will have to use Location change listener to cater this scenario, but this will drain battery.
If I go for device's timezone, User can change it.
Is there any other thing i can possibly do to restrict application to specific region?

You can also check for the network the user is registered on with TelephonyManager
You have 2 methods that can be helpful.
GetNetworkCountryIso
http://developer.android.com/reference/android/telephony/TelephonyManager.html#getNetworkCountryIso()
and
GetSimCountryIso
http://developer.android.com/reference/android/telephony/TelephonyManager.html#getSimCountryIso()
Explanation
getNetworkCountryIso() will give you the iso for the country which the user is currenty registered for.
ie: If you're from Albania (al) and went to travel to USA (us) this will return "us"
getSimCountryIso() will give you the iso for the country where the SIM provider's country code.. ie: If you're from Albania (al) and went to travel to USA (us) this will return "al"
UPDATE
You can integrate (if server side available) http://www.whois.net/ip-address-lookup/ to look for the device IP address. You can get the IP like this.
How to get IP address of the device from code?
With a combination of all this functions (Wifi, network provider, IP, GPS, Google Play regions) you can reduce a lot the use limitations of your app. In the other hand if the user it´s advance enough to fake the IP using a proxy, doesn't turn on the Wifi / GPS and doesn't have SIM card, there´s not much more to do.
Hope it helps :)

As a continuation to my comment, you could go by those lines of filtering users by country code.
The problem - only some carriers store the phone number on the actual SIM card. If so, you will be able to obtain it using
TelephonyManager tMgr = (TelephonyManager)mAppContext.getSystemService(Context.TELEPHONY_SERVICE);
String mPhoneNumber = tMgr.getLine1Number();
To avoid the instances of those carriers who don't store the actual number on the SIM - there is no way to retrieve the number seeing it is not stored on the phone.
So, what I would do, is simply on the first run of application, request the user to input his full phone number (including country code) - and store that in SharedPrefs. Then, you will know if to run the app or not.
Good luck, hope this has helped!

What info can I get during a phone call using the Android API?

Could I get MCC & MNC of the other party, either on an incoming or an outgoing call?
I am aware that you can get your own information from the SIM card but I am interested for the information of my contacts.
I guess I must be able to retrieve such information during a phone call.
So two main questions:
Is it allowed from the protocol?
Are there any classes inside Android API that provide such information? (looked up inside TelephonyManager but did not find any)

Like payeli has answered: No, you cannot.
Firstly, because there is no API for accessing the other party's cellular information. Secondly, because Android doesn't actually know. You can delve into the source code of the TelephonyManager, and you'll see that it only contains information about the local telephony provider.
Furthermore, the internal Android class Connection also shows no hint of any such information. (Regardless of the information it contains, it isn't accessible from the API, not even via reflection.)
That being said, there are currently services that provide some insight into phone numbers. Here in the Netherlands, KPN provides an API for looking up caller information, including the current coverage state of the phone, whether it's roaming or not, and other details. I'm not sure if the API is public yet or not, but perhaps there's a similar service available in your region.

No, you can only retrieve the MCC and MNC of your phone, not for third party numbers to which you make or recieve calls.
Reason: Calls target a phone number, not the MCC/MNC of the sending/receiving devices. The MCC / MNC tuple is used to uniquely identify a mobile phone operator/carrier, so if user is using carrierX at present, he will have one value of MCC/MNC, and if user changes mobile carrier/operator but retains same phone number, the the value of MCC/MNC will change but phone-number will still be constant.
So the mapping between phone number of a contact and MCC/MNC of their carrier are not fixed. So:
Could I get MCC & MNC of the other party, either on an incoming or an outgoing call? NO

ANDROID: Query Network Band frequency information

I need a way to determine which cellular network band my phone is currently on, and which tower it is connected to.
How would I go about doing this? I know there is a "Service Mode" you can enter with the command *#0011# --> however this does not work on my phone.
If there is a way to create an application where I can get this information, that would be ideal. I believe I would need to access the internal telephony classes of the android OS - which can be accessed via reflection.
Thanks

Take a look at these:
http://developer.android.com/reference/android/telephony/gsm/GsmCellLocation.html
http://developer.android.com/reference/android/telephony/TelephonyManager.html
You can get the CellID with appropriate methods within these classes. The CellID is a unique number for each cell (or each sector) so that identifies the tower. But relating that number with a specific tower (that is, its location) is harder, as that usually is not public information.
I'm not sure if you can get the frequency band, but if the "cell info" methods mentioned in the above links include channel numbers (ARFCN), you can deduce the band from those numbers.