Will a T-Mobile USA SIM work in a T-Mobile UK phone?

Question

I currently have a Motorola W377 phone (Tri-band: operates on GSM 900/1800/1900) and use the UK T-Mobile provider. I'm going to the USA soon and have noticed on their site T-Mobile are offering a USA sim card for $6.99. I am wondering if I have to get my phone unlocked to use it. Basically I want to put a USA T-Mobile Sim card in a UK T-Mobile phone. Will I need it unlocked?

Answer 1

No, the phone will need to be unlocked.

Answer 2

Handsets purchased in proper networks' shops in the UK usually doesn't work abroad with other country's sim card, so it's best to get your phone unlocked.

I travel to and from Hong Kong very often and I experience the same problem with my UK phone.