Nto sure if others have taken this approach, but we actually had our service contract language condensed by our attorney and added it to the back of our invoice.  It's a two-part invoice (white copy and yellow copy sort of thing).  The client gets a breakdown of their services, price, payment info and signature on the front and the terms on the back. 

A line above their signature reads something like "By signing below, I agree to be bound by the terms and conditions listed in the service agreement on the reverse...". 

It cuts down on the paper that's going back and forth and is one less thing to remember.  Everyone gets an invoice, so they automatically get a copy of the terms and conditions.