I am currently working with a supplier to provide pc to sms solution for notification of upcoming sales, notification their machine is fixed, ready etc.  
My problem is this...

The proposed SMS provider will be Clickatell.  

They can either have have responses go  to a dedicated mobile phone... or the alternative setup is for replies to go back to clickatell via Vodafone MSISDN.  I am trying to find out if anyone has used their service before and managed to comply with the SPAM ACT, via providing a free unsubscribe via same mechanism that was used to provide the promotion activity... i.e. free SMS back to sender?  

If using the NZ Telco gateways i know there is the 'free return' leg of the conversation, i.e. if its MO type message, then provide can say "thanks for your vote" etc, and for MT messages, the receiver can respond once free i.e. quit, unsub, etc...  

Of course the NZ telcos cost much more than the overseas providers, and therefore preference is to keep the cheapest option, but stay on DIA's good side...

any advice would be greatly appreciated.