I have an OBI200 with google voice and I am using a grandstream HT502 (which supports pulse dialing) to dial out through the OBI using GV. The HT502 is a little picky when it comes to accepting pulses. I am using a 500 set with no issues, my Uniphone is a little temperamental.
I got most of my info through obitalk forums, I can assist if you are interested.