03 May 2009


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...)


  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.

  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.

  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).

  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.

  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. :)

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

    SLO? Even nicer than Santa Rosa.

  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.

  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...

  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.


  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.

  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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