An Incoming Text Message from a particular contact-How to block?

Hi everyone,
I have always used nokia so don't know much about Android. Now, I have an android mobile which works like a dream.
I have more than 100 contacts. Few of them regularly send useless messages. I have deleted those contacts but still getting their messages. Is there any way to block there numbers for incoming messages.

Reply as soon as possible.

Hi,
This is really a problem that even you don't know the contact no. than also the messages are coming.
But, there is a way out for every thing. What you have to do is that just go to that no. and put it into the blacklisted contacts.
Neither you will get a message from that and nor any call.