Executive summary: mpirun hangs when laptop is connected via cellular modem.

Longer description: Under ordinary circumstances mpirun behaves as expected on my OS X (Intel-duo) laptop.  I only want to be using the shared-memory mechanism - i.e. not sending packets across any networks.   When my laptop is connected to the internet via ethernet or wireless (or not connected to the network at all) mpirun works just fine, but if I connect via my nifty new cellular modem (Verizon in case it matters), mpirun hangs at launch.  I.e. my application never even starts, and I have to use <ctrl-z> to interrupt to regain a prompt.   I'd like to be able to engage in other activities (mail, cvs, skype) while executing mpi code in the background, so I'm really hoping there is a simple switch to fix this.

I am launching with the command:  "mpirun -np 2 ./gx".   I have also tried "mpirun --mca btl self,sm -np 2 ./gx" but that did not seem to improve the situation.

I have attached the output from "ompi_info --all".  The output does not seem to depend on whether I am connected via the modem or not.

Thanks in advance.

- Tom