From my experience (and what I've read elsewhere, and it's also listed as a problem on telestial.com at least with Passport global SIM cards), GSM phones can SEND to CDMA networks (Alltel/CellOne/Verizon/SprintNextel) in the US. However, many (not all) GSM SIM phones based outside of the US cannot receive texts from US CDMA phones.

YMMV, but that's what I've encountered. In fact, Verizon Wireless can't even send SMS messages to every country. But they'll gladly charge you for the attempt. I got charged $1.25 for five attempts to text an Estonian mobile phone - Estonian carriers are not on Verizon's list of supported global SMS recipients. I had to spend 45 minutes on the phone to get that cleared up.