The current behavior of OpenBTS is to ignore the message.

OpenBTS does not advertise any parameters on its beacon that would indicate GPRS service.  Therefore it is completely reasonable for the system to ignore messages from a protocol that it does not support.  If the handset expects it to do otherwise, that would appear to be a bug in the handset, not in OpenBTS.  (Yes, handsets have bugs.  Plenty of them.)

On Feb 22, 2010, at 6:50 AM, Ben Wojtowicz wrote:

I have seen this behavior on other (non-openBTS) systems with some different phone models (definelty not with IPhones since I have never tested with one of those).  Anyways, after looking into the specs a bit, I determined that the best way to get around this problem is to just ignore the message.  The phone is not expecting a response to it, since it is just telling the network that it does not have a GPRS connection anymore.
Hope this helps,

David A. Burgess
Kestrel Signal Processing, Inc.