As far as responsibility, you will get the runaround. Rogers will say its Moto's responsibility, and Moto will say Rogers. Phone providers will tell you that the
SIM lock is placed by the service provider. And many service providers refuse to unlock "their" phone for use on another company. Some cell companies are actually sueing to try to keep their phones locked, even though you baught it!
So when it comes down to it. If rogers unlock it wont then the responsibility is yours. Or buy a new phone for Tmobile.
One way to try to find a somewhat reputable company is to do a search on ebay for unlocking services. That way you can check their feedback and have a better chance that nothing shady is going on.
I did a search on ebay for "v551 unlock" and came up with many options. All with excellent feedback.
This is one example. $25 with 99.5% positive feedback. My discaimer. I chose this company at random and have never used them or know anything about them.
http://www.unlocktotalk.com/moreinfo.html