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Next VOIP Project: SIP-GSM Gateway

The other day I called my cellular carrier, T-Mobile. They tell me that I can convert my plan to a “family plan” and add another phone. Further, it’d be ok if I provided the phone myself, perhaps an old GSM phone that I haven’t used in a while. I have an old Razr sitting a drawer somewhere. But I have other plans for the hardware.

I have a huge number of minutes on my plan as I often use my cell for tech support work that can go for hours. Then this week the US cellular market is rocked by new offers of “unlimited” minutes for $99/mo. That’s what I presently pay for my 2500 minute plan. Might have to change that plan soon. This just makes me think that I really should go forward with a plan to add a SIP-GSM gateway to my Astlinux setup.

Since we dropped our last POTS line I’ve held onto one account with Nuvio for our home phone line. Nuvio provides a 911 solution for VOIP users. It’s not great solution since that account is $50/mo for unlimited domestic long distance. We don’t use that many minutes, probably less than 300 a month, and mostly local calling at that. Not great economics.

If I could add a GSM gateway and change my T-Mobile account to a family plan then I could use the GSM network as a backup to my less costly, pay-per-minute usage-based VOIP providers. Setting aside the cost of the gateway device it would also be cheaper to operate, based upon dropping the Nuvio account. It would also provide a 911/411 solution.

Finally, it might allow me to provide a sort of DISA capability for use along side our OnSIP hosted PBX. I could call back to the number assigned to the gateway device, authenticate against my server then dial overseas numbers at IP based calling rates. That would save money as well.

The leading contender for the GSM gateway device is the Portech MV-370. It runs around $250 and seems to be well documented as working with Asterisk. There are cheaper GSM gateway devices but they bridge GSM to an analog port. Going all the way back to analog means I’d have to add an FXO to my Astlinux server. That’s not going to happen. I’ve had terrible experience with small format FXO adapters.

Besides, staying in the digital domain means better call quality. No problems with echo or interrupt conflicts, etc. It’s just better. Well worth the $120 difference in the gateway cost.

The hardware will be delivered in about ten days. It should make for an interesting weekend project.

This Post Has 5 Comments
  1. “I’d like to provide my own 911 and 411 service by bridging calls over to my cellular account.”

    Oohh….I see these on eBay all the time (FXO ones anyhow). I had kicked around the idea of getting one for the free mobile to mobile minutes. I wasn’t convinced to do it. Your 911 idea was an advantage I hadn’t thought of though. All the location identifying stuff is already solved with cellular. Nifty.

    Of course there’s the problem of how do you actually test it? 😉


  2. Looking forward to your experiences with the GSM gateway. I was considering something similar using chan_mobile and a bluetooth phone, but the gateway you ordered will no doubt be a more robust solution. I’m assuming that all outgoing calls through the gateway will end up with the mobile service number as outgoing caller id. Do you know otherwise at this point? That may be a big negative for some.

  3. The hardware is on its way now! No doubt there’s a lot to be learned along the way. A solid 911 and 411 solution may be at hand. Ideally I’d like a 311 solution as well, but cellular carriers don’t seem to provide this.

    I saw the GSM>analog type interfaces, and they are about half the cost of similar GSM>SIP interfaces. However, staying digital seems a lot more attractive. I never want to fight with FXO tuning again.

  4. The hardware arrived a few days ago. So I hope to get underway with the project this coming weekend. I’ll post progress reports here on my blog.

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