SMS via Wi-Fi or Two-Phone Activation

[roheer]

I recently switched to the Treo 700p and I regret my decision somewhat. The deciding factor was being able to respond quickly with one hand to a text message or email. However, when I don't need to respond quickly, that nice big keyboard on my PPC-6700 is such a convenience. So here's my question: Is it possible to send text messages over a wi-fi connection through the manipulation of the radio settings, or with a different program? Or even better, can I somehow use both my PPC-6700 and Treo 700p on the Sprint network, if I was only keeping one cellular radio on (thus only making it look like one phone was registered)?