The 3.0 CTP EULA, as far as I can see, makes no mention of text chat at all. Granted you still have to comply with any laws about text chatting and encrypted text. I don't know if the Zune wireless is encrypted or not, but that would be something to look into if you wish to comply with the EULA and laws.
Do note that this is just the EULA for the CTP; the 3.0 RTM EULA will be a different EULA so you'll have to re-evaluate things again at that time.