Android as SIP to GSM gateway

Question

Soon I could use a SIP to GSM gateway, because I'll need to make phone calls from Germany to a mobile phone in Czech Republik. Hence, I thought about implementing one.

Now, the questions are:

• Does such a solution already exist (for a reasonable price)?
• Is it possible to redirect a (voice) stream to a GSM connection with the available Android APIs (SDK or NDK)?

Ideas, suggestions, comments are highly welcome.

Solution 1

You can solder the adapter, which turns the microphone input on the headset into a line input. In the headphone jack, such an adapter is inserted, which physically routs the audio output to the headphones into the microphone input of the smartphone. Together with the application, you just need to show the electrical scheme to solder such an adapter or sell an adapter on the Internet.

Solution 2

You can use asterisk with chan_mobile and connect your android (or any old mobile phone) to it via bluetooth. This is reasonably priced if using a Raspberry Pi.

Strictly speaking this does not satisfy the Android requirement, but rather uses any mobile + bluetooth + asterisk as a GSM gateway.

http://www.stocksy.co.uk/articles/Networks/use_an_old_mobile_phone_as_a_gsm_gateway_in_asterisk/

Solution 3

To date most android devices are not architected in a way where both sides of the in-call audio are available to apps running under linux on the application processor. Instead, the in call audio seems to be private to the radio processor.

Solution 4

It's not possible to use Android as a SIP GSM Gateway. It is possible to make calls but the API won't let you redirect incoming audio to another stream or send your desired stream as outgoing audio. It will be limited to device microphone/speaker and bluetooth/wired headsets.

The Android Telephony package passes the complete control of radio device to Radio Daemon (rild) library which would not allow you to change the audio streams as mentioned above. Even, rild is vendor-dependent propertiary software and is not opensource, so using Custom ROMs would not help.

For more technical info, see here.

Solution 5

in the case you use a computer for managing sip calls, you can "transfer" voice and control your phone with bluetooth.

View more solutions

Comments

[Admin]

My goal is to call my Android phone via SIP and let Android forward that call to a different mobile phone.

[marczoid]

Then I don't understand the issue. If you call via SIP, the other mobile phone needs to receive the call in SIP. If you want the other phone to receive it over GSM - you need a gateway in the middle.

[Admin]

I'll do an example: I live in Germany and person P lives in Czech Replublic. My Android phone with CZ SIM card is in CZ and I do have high speed internet in Germany. Now I want to call P on his CZ mobile. My idea now is that I would call my Android phone located in CZ using SIP. The phone would then establish a GSM connection with P and forward all the voice payload in both directions.

[Bernd]

You probably would come out much easier if you drop the android and gsm requirment. A desktop PC with appropriate interface hardware connected to a fixed telephony line would be much easier to set up, e.g. with asterisk.

[garima]

@martin-so are you saying that this would include 3 phones?first would make call from SIP and the other is on GSM .You want an interface between the two phone by creating a gateway

[Admin]

@all: Sorry for the delay, I started a new job this month.

[Admin]

@Bernd: It depends how expensive a GSM card for PC is. I'll think about it, thanks.

[Admin]

@Garima: I'd like to call phone B from phone A. Phone B would then call phone C and forward the voice streams in both directions. Hence, yes there are 3 phones involved.

[garima]

@martin-so basically a call forwrding technique is required on phone C..Sip support is available now in android ..