The problem might be that for some, dialing +1 makes calls not go through. For some (like myself), it causes no problem. That's what makes it so confusing to troubleshoot.
A workaround was added to the RIL a while back (commit
here, if you're curious). Try adding
to your cmdline (startup.txt). If the problem is with the +1, and if that fix works for TP2 (it should, but I'm not 100% sure), that should solve the problem.