Is it possible to have more than one APN active at the same time? It seems to me like you can create multiple GPRS bearers (not yet tested), but the TCP sockets then don’t seem to have any method to determine which APN is belongs to. In particular, if I host a TCP socket and have multiple GPRS bearers active, will both APNs be able to connect to the module? This is not desirable.
Multiple GPRS PDP context is possible, yet wipLib seems doesn’t support. You can have a single WIP_BEAR_GPRS option.
If you can really get GPRS service with multiple GPRS PDP context support you may try with :
on UART1 send ATD99*1# to activate context #1
on UART2 send ATD99***2# to activate context #2
I would also want to know if this is possible… 
I have also thought of this. Will test it sooner or later and post results.
Only trouble is I’m on a closed APN bu talso want to use an NTP server (and other serivces) on the public APN.
Also, using the two UARTs as standard dialup links on two contexts would add some complexity to the design (suddenly 1.8V logic levels need to be possible).
But, I suppose if the external chip can run its own TCP stack and also run one for each UART, the problem is solved and you have two nicely isolated GPRS links. One secure APN and the other open internet.