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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.

Bill the Lizard
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  • Does Android allow for a "multihomed" setup, i.e. one ethernet interface via WiFi and one via GSM in parallel? – Bernd Jan 18 '11 at 11:52
  • I've no idea about the abilities of Android, that's why I'm asking. I was hoping to find some experienced Android developer who could point me into the right direction - or tell me that's not possible at all. –  Jan 18 '11 at 16:11
  • Forget my question. You do no need a data bearer on GSM, so yo don't need ethernet on GSM. You need a GSM voice bearer. So the question rather would be: does Android allow access to telephony voice payload from applications? – Bernd Jan 21 '11 at 06:35
  • Yes, that's almost correct. I need to establish a GSM connection and access the incoming and outgoing voice streams from an Android application. –  Jan 21 '11 at 10:00

7 Answers7

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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/

Pranab
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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.Android VoIP Gateway

eGregory
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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.

Chris Stratton
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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.

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

kaiserzoze
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This is not a question for Android but rather to the gateway side. Android will be dialing out using SIP through a 3rd party app or through the one provided in its SDK, but then the transcoding and redirection over GSM is done on the gateway side.

Tsahi Levent-Levi
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    My goal is to call my Android phone via SIP and let Android forward that call to a different mobile phone. –  Jan 20 '11 at 14:47
  • 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. – Tsahi Levent-Levi Jan 20 '11 at 15:47
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    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. –  Jan 21 '11 at 09:58
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    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. – Bernd Jan 21 '11 at 21:35
  • @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 – garima Jan 27 '11 at 08:56
  • @all: Sorry for the delay, I started a new job this month. –  Feb 09 '11 at 17:04
  • @Bernd: It depends how expensive a GSM card for PC is. I'll think about it, thanks. –  Feb 09 '11 at 17:05
  • @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. –  Feb 09 '11 at 17:08
  • @martin-so basically a call forwrding technique is required on phone C..Sip support is available now in android .. – garima Feb 10 '11 at 08:43
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There is a solution can make your Android phones work as SIP GSM Gateway for calls termination and origination

http://pure-voip.com/

Sam Jolan
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