I asked at the MTS store in Brandon Shoppers Mall last week (July 2012) and the service person seemed 'shocked' that I would want to unlock my MTS BB, even though I explained it was so I could use a SIM card in Australia and avoid roaming charges (acc to both MTS and the Aussie ph co's my BB will work in Australia).
There are many unlock providers on the WWW, some that specialize in BB and some that specifically will unlock Canadian BBs including MTS. The reputable ones will likely charge more for a MTS BB as apparently MTS uses a stronger lock than say Rogers or Telus. Do not use the free services as many of these are scams. There is also a Russian-based one that seems to be claiming to be MTS endorsed; its not.
Cellfservices seemed the best of those I reviewed and has a YouTube video on how to do it, but I haven't tried them yet. http://www.cellfservices.com/
I was told that for a fee Rogers will unlock your Rogers BB, IPh or Android.
MTS as usual is NOT interested in customer service, only ripping its customers off. Well, I guess that's true of all Canadian ph companies.