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)

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!

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.

Check mobile data connection/signal before doing HTTP request

In my Android application I first get the users location using either GPS, the GSM network or a text value that is manually input via a Settings screen.
At first I used the Geocoder class to get the users locale with latitude and longitude provided by GPS or GSM but it seemed unreliable, now I used Google's web API to get the locale by making a HTTP request and parsing the XML document returned. This is using the following URL:
http://maps.googleapis.com/maps/api/geocode/xmllatlng=blahblahlat,blahblahlong&sensor=true
After getting the users locale I then send another HTTP request to free.worldweatheronline.com's weather API and parse the XML returned. With a stable internet connection the application runs fine, however my house has a rubbish signal and even worse mobile data connection.
I am aware there is a simple method to check if the device has a mobile data connection, however what I want to know is whether there is a way of measuring the signal strength as the problem arises when there is a connection, but it is too bad to successfully run. For example, if there is a way to get mobile data signal strength which returns a value from 0 (no signal) to 100 (full signal), I can then only carry out the location and weather retrieval if signal strength is above a certain amount.
Would it be best to just surround the location and weather retrieval code with a try/catch so it doesn't cause a runtime exception, allowing it to just fail gracefully then update when a better signal is acquired? Any ideas on how to accomplish this, or any other suggestions to make my app more friendly for users with bad signal?
Thanks in advance!

You can check it but remember to handle, in any case, drop of connections.
In my apps I had some problems while writing files or stuff like that with an open connection, so just remember that a fail may always occur (for example switching from gprs to wifi).
If you can easily check the signal strength I would do both.
Give a look at the SignalStrength class (never used it btw). Here a nice explanation.

You can check cell service signal strength by creating a PhoneStateListener and handle the onSignalStrengthChanged callback. For more info look at this question How to get cell service signal strength in Android?
EDIT :
You can pause PhoneStateListener by calling telephony.listen(listener, PhoneStateListener.LISTEN_NONE); to not receive updates when you don't need them.

How to detect available carrier networks?

Is there any way in Android to detect all available carrier networks in the area. I tried to search it from connectivity manager and it seems it only returns active network info. I also tried the telephony manager and it only returns signals and neighbor info of the active carrier (e.g. other signals of same carrier). I would like to create an app that will scan for available cell networks in every country -- like in Settings -- to choose my network when roaming.

as far as i know that is not possible, because you can only get the cell info of your SIM carrier, but we have a new method on TelephonyManager called getAllCellInfo ().
The problem is that method its only available on API Level 17, only available on devices with Jelly Bean (4.2).
Check this link for more information.

Even the getAllCellInfo function will never report "all networks" that are in the air at your location, simply because the phone will only listen to / measure on the frequencies / networks that the current serving cell tells it to measure on. Normally this means that it will only measure (and be able to report cells) from the same network as the phone is currently using.
If the phone has lost coverage from its "home PLMN" (home or selected network) it will however periodically do measurements in other frequencies to try to get back to it's "favourite network".
To be able to get lists of all present networks in your area you need to have another kind of device for example a "scanner", which never locks on to any cell, but continuously scans many frequencies to find cells from any network and any radio access technology (GSM/WCDMA LTE for example) within these frequencies.
Or continuously press the "select network" function...
/ Kenneth