If you can provide call reference IDs for the calls where your adapter reboots, support might be better able to diagnose the issue. (I assume that if it connects enough to ring, you'd see the call in your logs.) Any chance you can exchange the RT31P2 for a PAP2? I understand not opening a ticket on the first event or two, but once you are sure enough that it's a recurrent (even if seemingly random) issue, it's definitely worth filing a ticket.

I understand and feel your frustration regarding 'number not in service' messages... I got one yesterday, as well (didn't file a ticket b/c it connected when I tried again).