The value exchange is out of balance. The advertisers get what they want, but too often the consumers don't often get anything of significant value in exchange for the opt-in. Companies assume that when people opt-in, that they want to hear everything from that brand. This may not always be the case, which results in unsubscribes and consumers who just ignore and delete.
When a customer opts-in, this is not traditional advertising where you broadcast the same message everywhere and hope for a small percentage to act on it. This is your time to show these customers you truly value them. Offer your text-message subscribers something more than the general public will receive. Give your "fans" a reason to follow your facebook updates. Most importantly, encourage these opt-in customers to talk about you and share with their friends.
It's about building business, right? So make these fans of your business fanatics. Don't just buy your time with them until they give up on you.