Try Cell Signs. We are trying their Mobile Agent solution. Live in a less affluent county and hope the text idea works for most cell users.
Just got up and running. I am testing the service and hope to launch with rack cards, paper stuffer, a press release and of course web ads.
Sign up is awkward, You get 3 texts. But one done works great.
They have a demo you can use. If you call ask for Heather.
Go to CellSigns(dot)com and go to the Mobile Products on the right.
FYI I am a new customer of their's. I don't work for them. Only issue I have is it's very pricey. However, you get access to the entire mls via text. Also in our market most people wont have a smart-phone yet.
You are welcome to call me anytime and ask about how it is going or email me.