I finally decided to go with OTR Mobile, although I ordered a MOFI 4500 rather than the devices offered by OTR - it looked like a better unit. The MOFI arrived today and the OTR SIM card should be here Monday or Tuesday.
I may start a separate thread so I don't step on this one by TheMan419, especially since he's been so helpful.
I will say, the OTR folks are VERY responsive and helpful.
Somehow I thought the MOFI had an indicator for signal strength, but no. I guess I'll have to do some trial and error with my phone.