Why is my D6603 Carrier Locked?

[AC Question]

Why is my D6603 Carrier Locked

Opened a brand new Sony phone, put in Sim Card. After opening Android logo, an MTS logo with blue font and white background pops up. Then it simply states "SIM service provider unlock PIN.

I called MTS in Canada, they have no record of the IMEI number. I called Sony, they told me to **** off 'cus I'm out of warranty. All I want to know is who my bloody provider is. I called T-mobile UK, Verizon, T-mobile US, numerous others and they told me they cannot explicitly state if the phone was ever used with their service.

I am extremely confused, I wanted to use an unlocking site, but alas. I entered *#*#7378423#*#*, went to Service info and then Sim lock. It was as follows:

[] Network 0
[] Network subset 0
[x] Service Provider 5
[] Corporate 0
[] Sim 0

I am wondering if anyone can give me any idea what is going on? My IMEI # has no problems, it is: [removed by mod]

I am not sure how to proceed and get this working again. I entered a T-mobile US sim card. Please Help.

 

[B. Diddy]

Welcome to Android Central! Where did you get the phone from? If it was some independent seller, are you able to find out from them?