Default [Q] Best SIM unlock service for Xperia TL lt30at

I'm curious to know what everyone's opinion is about a reliable, and preferably inexpensive, option for SIM unlocking a Sony Xperia TL (lt30at) currently locked to AT&T. I've attempted to have a family member (with a current good-standing account) call AT&T with the IMEI's, but they were told that the phone needed to be on their account with a mobile number attached in order for them to give an unlock code for it.

With that said, it seems that I'm in the market for an unlocking service, so are there any services that can do this for me inexpensively? I've found the following site offering unlocks for this device for $29.99 USD:

So far, this is the lowest I've seen, though I haven't looked into the legitimacy of it yet since I wanted to see if there were any other comparable offers out there.

Any suggestions would be greatly appreciated.

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