Here's my situation. I switched to Verizon in mid-November. After three or so days, none of the text messages that I would send to one friend would go through (they did when I first switched). Nothing changed with his phone and nothing changed with mine and I can still receive messages from him. The same thing started happening with my brother but I am not sure when because we don't text frequently. Neither are with Verizon but I think they have different carriers from each other as well. Anyway.
Today I spoke with a Verizon rep to see if we could get it figured out. He asked me to try sending picture messages to both people. The picture messages went through without a problem. I immediately tried sending a text through after that - one went through to my friend but not my brother. My boyfriend suggested I try sending through vtext.com to see if it is an issue with my phone. When I enter my brother's phone number, I get the status message "Delivery to this destination failed due to invalid address." I know the address (phone number) is correct and Verizon recognized it for the picture message that was able to go through. Any ideas? Has anyone else experienced this?