Well, I have a pre-paid/pay-as-you-go Passport SIM, just a global roaming SIM with a UK number. I already know my Verizon phone can send to it, but the info with the SIM specifically states it cannot respond/send to CDMA carriers. Lame.

I'll be picking up a SIM in Ireland in about a month (probably Meteor, they seem to have the best pay-as-you-go option for my needs) and I'll find out how well Meteor works with texting home to Verizon Wireless and T-Mobile USA.

Have you thought about using a WAP webmail sevice like Gmail? All you need is a cheap, low-speed web connection (like T-MobileWeb for $5.99/mo unlimited). I think doing that would finesse the network interoperability issues, since email is the messaging lingua franca of the internet.

It's not in the contract, but mine works in Europe without data charges if I make sure the phone registers on a T-Mobile site by manually selecting "Network."