Develop Reference

How can I bridge phone calls to VoIP?

I want to have one stationary device like an android phone that can use a standard local SIM card and forward all calls to a second device over some kind of VoIP protocol. When someone calls the phone number of the stationary device, I want my second device to ring and handle the call through something like linphone, element, or whatever. Ideally, it should be possible from the second device to initiate a call from the stationary device's phone number as well. Bridging SMS too would be nice, but I already have a solution for this on android.
There are many use cases like
when traveling abroad, being able to bring the latter device and receive/make calls via the stationary device at home
forwarding multiple phone numbers to a single device and e.g. switching off the work number when away from work
having privacy when the location of SIM cards is logged, by making calls over wifi from somewhere else than the stationary device
when traveling somewhere with bad mobile coverage but available wifi, without having to think about how the second device handles it
Are there any existing projects for doing this?
If not, then what would be necessary to make something myself? Is the best solution something like connected an android device by bluetooth to something running asterisk like was discussed here? Or has something changed in the past 11 years, maybe the existence of some working linux phones makes this possible on a dedicated purism or pinephone device?

I think you can achieve this with Brekeke SIP Server. I am using their solution to achieve something similar to what you want to do.

there are multiple ways to achieve it technically, but the most practical solution to your use case will be to use a VOIP Gateway device.
Actually we can not use a mobile phone as gateway between SIM and VOIP calls.
so you can buy a voip gateway example GOIP (single SIM) and put your sim, connect to your home internet and configure. your phones softphone (eg linphone) will be able to directly register on it and you will be able to make/receive calls and sms.
there will be a new problem as mobile OS platforms are more and more restrictive about power, your sip client will not be able to receive calls while in background for that you will need push, so you can use twillio's mobile sdk to make a client that works fine then forward your calls to twillio from gateway. since there is no number or telecom services involved, cost on twillio should be minimal.

A more common way to do this is with an operator service, rather than implementing it yourself.
The operator is able to see the routing to your number and simultaneously call multiple numbers you have set up. Different operators will have different names and details so you would need to speak to your local operator.
For example BT in the UK (who I have no affiliation to - just an example) provide a service called 'Follow ME': https://support.ringcentral.co.uk/s/article/9010?language=en_GB
If you do want to do it yourself than an open source PBC like Asterisk is indeed a good starting point.

Is it possible to send an SMS from Visual Basic 2013 through my smartphone?

I would like to send an SMS from a VB2013 application with my smartphone programmatically. I have already found several solutions how to solve this with Windows Phone (Outlook-Windows Phone). The only problem is, that I have an android device. So my question is, do you know any idea or solution that supports android?
The workflow that I want to implement is the following:
The user types into a textbox the phone number and the text on a VB2013 app.
He/She clicks to the "Send" button, and somehow it sends an SMS from the android phone to the phone number that is given by himself/herself.
Regards,
Roland

I would say that this is not possible directly.
The problem you already found is that your Smartphone is Android and
Vb.Net needs a .net Framework with which it works.
So the possibility I see is to get a connection
via USB port to your device and send some specific commands to
make your smartphone send SMS. To do this you have to use a serial port from
my point of view.
This question has already been asked, so
please take a look at:
Sending SMS with Vb.net

The .Net framework does not natively run on Android, so no this is not possible.
However, the Xamarin framework allows you to write android apps in Visual Studio.
Specifically towards your question, Xamarin has an SmsManager class that allows you to send Sms messages, the documentation can be found here.
Hope this helps.

There are several different ways to do this, but the best one is use an api like Twilio. You can literally send an sms with one line of code. They have a nuget package which would get you up and running even faster.
Another is to use carrier mail. You have to know the users carrier and then you can create an email address that sends as a text ie. 1231234123#txt.att.net. The issue with using cellular carrier email is that spammers often use this and one minute there is a message from your site and then next is spam, since it will be coming from the same carrier.email address.

Simulate incoming call on own android device

I want to fake an incoming call on my own (physical!!! -> not the emulator) android device. I know there are lots of apps that actually can do that, which means it cant be that hard - I just need a hint. Searching the net only brings up apps which do the job.

Android Phone-to-Phone Communications

This is more about an explanation then it is about asking a question. What I am wondering is if its possible to write an Android application that can communicate with another Android phone, given the phone number of the phone I want to communicate with. By communicate, I mean I want to be able to send data to the phone and have my application on the other phone be able to recive it.
If its not possible to do this, then I guess my alternative is to have my application "sign" the phone into a server. Then I'm assuming the server can act a proxy to communicate with both phones.
Any clarification would be helpful!

Check out the BUMP api. It allows you to establish a connection between two (I think more are also possible) devices, and it gives you a channel over which to communicate. The devices need to be "bumped" first, but then it's all fair game.

Any reason why it has to be by phone number? That and i'm pretty sure you can only send data over WAN or local bluetooth/wifi.
Perhaps try something along the lines of a server that has phones sign into it and keeps track of the phones IP addresses allowing them to communicate almost directly to another (kind of like a dynamic DNS hah!).

Look into SMS. I haven't coded for mobile phones in years but I seem to recall that most phone operating systems let an app intercept SMS messages, react to their contents, and prevent the user from seeing them.
As long as you're not sending lots of data, SMS might do the trick.

How to do Client server communication in Android?

I want to send and receive information between Emulators in Android.i am using two systems and i have installed android in both the systems and i have to consider one emulator as server and another as client.Now i want to send data from one to another.Anyone knows regrading this please help me with some sample code.

What sort of information do you want to send between the emulators?
You can transmit SMS messages, or simulate phone calls, from one emulator to another using the target emulator's console port number as the number to dial. The Android Developer Site describes the process in more detail under "Sending a Voice Call or SMS to Another Emulator Instance"
If you want to transmit data, unfortunately Android doesn't currently provide any P2P or Instant Messaging APIs, so there's no generic technique available through the SDK you can use.
Your best alternative is to create your own server-based solution (or your own P2P API, though that might be a little more complicated).

Take a look at Java Socket.