Some phones have blocking mode feature, which will allow you to block all or certain types of notifications, calls, texts and messages. To disable it, just go to Settings and look for Blocking mode option and then click Disable.
But if there's no unblock option in your phone, it is most likely managed by your cell phone carrier. For your convenience you can call your network's customer care to take that text message blocking on your account.
Or you may try it online (like for T-Mobile subscribers), you can log into the primary account holder's to remove the block feature.
Usually, you may encounter message blocking with commercials numbers or those using short numbers (XXXX), as they may be used to charge your account for premium services.
If you’re already paying for a text messaging plan or it’s included in your overall plan, perhaps you’re not in need of the mobile Web. Check out some text messaging tips that will help you maximize your plan without having to pay extra for Internet data usage at About.com.