LeJon,
Text is becoming a common form of communication and more common with the younger crowds. I use text to communicate with some tenants and clients but only after a relationship is established and one of us mentions texting.
With that said I dont think you are missing any business opportunities because any serious potential customer will probably not text an add as a first means of communication. If they are serious they would call unless you mention in the add to text as some people do (I know you didn't).
But I wouldn't be suprised if someone texts me about one of my rentals on craigslist. Are you putting Call # or just the phone #? That might cause some people to text the number.
But a texting plan should be cheap. Maybe you should look into it. If it helps you close one deal then it would pay for itself 50 times over.