03 May 2009

Pre-Paid

Last week I was in a close-out store and found a bunch of Net10 prepaid Nokia 1600s for $20 each.  At first I thought I'd found a good source of cheap handsets for testing.  I got one home and even though I provisioned it in my OpenBTS system, and even though it registered and showed service, it refused to place a call without any minutes in its "tank".

Here's what I did find, which may be of interest.  First, the SIM was generic-looking, no corporate logo, just the letters "SIM" printed on it.  Second, when the phone tried to register, the IMSI was from AT&T: 310410226242003.  Third, the phone rejected other SIMs, including other AT&T SIMs.  The handset appears to be keyed to a specific SIM, so to get this handset to act like a normal phone I'd need to get it rebranded, not just unlocked.  Fourth, menus in the phone showed the IMSI, the IMEI, the phone number and a "random number".  That was unusual, since a handset normally does not know its own phone number.  I am also eager to see if that "random number" is really Ki.

So I won't be buying a big pile of Nokia 1600s at Big Lots, but I'm keeping this one phone because it will be a great opportunity to see how prepaid phones interact with the network.  Hopefully, in a couple of weeks I'll have a chance to play with that, unless some other OpenBTS developer out there beats me to that.  (Hint, hint...)

12 comments:

  1. Wow, that different to the prepaid phones we get in Australia. Here the phones are just normal carrier locked phones. Everything else is done carrier side. You can even put a postpaid SIM from the same network - good for a cheap replacement phone.

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  2. That's what I was expecting here, too, which is why I was initially excited to see the phones in a close-out store.

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  3. I get the feeling that NET10 is a special case. They are operated by TracFone, which seems to do unusual things to their phones.

    If you can jump on it, there appears to be a discount of T-Mobile Nokia phones at Target (http://www.howardforums.com/showthread.php?t=1527354).

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  4. Holy crap! Thanks. I'll run to Target tonight.

    BTW -- I just passed through Santa Rosa on my way back from Sebastopol. Lovely area.

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  5. Let me know if you snag any. I go to college in San Luis Obispo and the nearest Target is in Paso Robles (about 30 minutes away).

    Yes, Santa Rosa is a lovely place. Also part of the former (and it seems re-emerging) Telecom Valley. :)

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  6. No luck in Fairfield or Vacaville. But Target does have pre-paid GSM phones for $20.

    SLO? Even nicer than Santa Rosa.

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  7. Radio Shack and big chain grocery stores (Ralphs, Vons) seem to have the low end Go Phone and NET10 phones. The Vons here seemed to have a few $20 NET10 (those and the Tracfones they had will probably be the most peculiar). I think the GoPhone that they had was the $30 (discounted to $25) Nokia 2610. I picked up a Samsung A137 GoPhone at Radio Shack about a month ago.

    I've kind of gotten an addiction to cell phones (and collecting SIM cards...). :)

    From my observations, the NET10 and TracFone are exclusively prepaid (they may actually have "post paid" plans) and it seems like they have custom software as a result. The pre-paid phones from the GSM Big 2 seem to be regular locked phones in different retail packaging. I think most of their functionality is accounting software on the carrier's backend (i.e. stopping a call being placed and playing an error when balance is too low, preventing GPRS/EDGE/UMTS access when balance is low, rejecting messages when balance is too low, etc.).

    I have not purchased a NET10 phone, but I think that the next time that I go in to Vons I will snag one.

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  8. There are 3 kinds of Locks in GSM phones:

    - SIM Lock, the case here, meaning a specific SIM
    - Network Lock, whats usually called "SIM-Lock", even if it's just locked to a Network, like the iPhone.
    - Country Lock, could be used to lock the Phone to SIMS from one country, althoug i never heard that this beeing really used...

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  9. I very much doubt the random number is the Ki. What would the SIM card be for then? Also, I fail to see in what way the phone behaves differently from a SIM-locked phone.

    If you think there's something really strange going on here, you could provide me with a firmware dump and I can have a look.

    Cheers,
    RPW

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  10. Have you tried to activate the Net10 phone, add airtime tank credits, then use it on the OpenBTS network? I wonder if it would take airtime tank credits out when making calls through OpenBT? Or if it does some sort of accounting through the AT&T network. Either way you should be able to see what its doing in the logs.

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  11. Net10 is using a special proprietary firmware on their phones. The only way to fully unlock them is to flash the firmware with a regular one, which requires expensive hardware.

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