There are couple of things we usually do for SMS spammers. You may try these out if you are keen, but do note that we take absolutely no responsibility over anything that you are going to do.
First, help them subscribe to lucky draws, events, promotions, and everything that needs a mobile number to work. Usually service provider would require the owner to reply with an SMS as a verification, obviously this will not happen but you get to send them the first "spam" for "free".
Second, if you get hold of two spammers, connect them using free VOIP services (those that let you try out the quality and such), enter spammers' numbers instead of yours and let them talk to each other.
Third, post the numbers and contents that you have recieved so far as comments - we are collecting statistics and we need your help with the supply of fresh spams.