I have this problem with Verizon. I've had it since long before I installed CM7, actually I've had it since before I even had the Droid Pro, it also occurred with my BB Tour (I do NOT miss that phone). It happens every time I reboot the phone. The easy but annoying fix is, after your phone starts up, just go to Wireless & Network settings, Mobile networks, Network mode, and switch to another mode and then back again. E.g. if you are on CDMA/EvDo auto, switch to Global, wait a couple of seconds, then switch back to CDMA/EvDo auto. You should be able to send texts now.
I really think this is Verizon's fault, since it also happened on my previous phone, but then again that might just be a coincidence. I am getting a new phone in about a month, if it has the same problem, I'm leaving Verizon.