LOCKED HANDSETS!!!!!

I recently had my handset un-blacklisted, but for some reason i cant use other networks sim cards in the handset. So i am thinking it is network locked, but when i queried this with one of the sales people, they looked at me like im mad and said NO WE DONT LOCK HANDSETS ONTO OUR NETWORK. Now what i want to know is why does the sim card work in other handsets but not mine(to be specific its a Vodacom sim) And if MTN dont lock handsets to the network, why do they have this on their website :<br> <br> HOW TO REMOVE NETWORK LOCK ON PHONE<br> \This service is for MTN contract customers only. Phone 173 or visit an MTN store and get a Network Unlock form. You will be charged R570 to unlock your phone. The money must be deposited into an MTN bank account