Sending And Receiving(?) SMS

[SChaput]

I have a small script on my website that allows a person to enter an SMS Number. Depending on the number it adds the appropriate email extension to their number. (ie ##########@txt.att.net) This sends a text message to the number formatted like this, "FRM: Apache User. SUBJ: (specified by sender). MSG: (specified by user).
Would it be possible to make it so the receiver could respond to this text message in anyway?
Thanks.

[tfit]

I don't quite understand what you mean with respond?
Respond through mail or sms? Do you provide a sms number to respond?