US cell phone in UK

I have a T-Mobile pay-as-you-go cell phone I got in the US (it's a Samsung Stripe, if it matters), and the specs say it's tri-band.  So in order to use it once we get to the UK, what would I need to do?  Can I just buy a T-Mobile SIM card once we get there, pop it in, and be good to go?  If I wanted to use a carrier other than T-Mobile, I'd have to get it unlocked, right?  We intend to continue using pay-as-you-go service in the UK, and I'm not terribly bothered about what provider we have since we don't use our cells much.  I just want to get my phone usable asap when we get there so I can have a contact number for house-hunting!

Thanks!

I had a T-mobile phone in the US and because it was tri-band, I assumed that it would automatically work in the UK (just as my UK tri-band phones have always worked in the countries I've visited - US, France, Belgium and Guatemala). However, when I came back to the UK for a visit in July it wouldn't pick up a network signal here and so I couldn't use it, so I'm assuming I should have done something in order for it to have worked.

I would call your T-mobile service in the US and find out what their policy is for using phones abroad and how to unlock your phone. They can probably set it up for you so that it will work in the UK when you arrive (note though that T-Mobile UK is not actually connected to T-Mobile US in terms of phone accounts, so there's no guarantee that a UK T-mobile SIM card will work in your US phone - the fact that I had a UK T-mobile phone had meant nothing when I joined T-mobile in the US). However, it will be expensive to use your US phone in the UK, so getting a UK SIM card would be a good idea.

When I arrived, I got a Sony Ericsson PAYG mobile for £10.  If T-Mobile in the Us won't help you, I wouldn't worry because there are many cheap mobiles around here.

I used to work for T-Mobile.  I know if you had your phone for over six months we would send you the unlock code no problems.

I am not sure if that policy has changed or how it affects PAYG, since I worked in the contract department. 

In the end I didn't even need to unlock it, when I got here it just worked. 

If it needs unlocking there are loads of places in the UK that will do that for what is probably cheaper than the charge from the phone company.

Vicky

It was free from T-Mobile for contract people, not sure about payg.  You can always call and ask.

If the T-Mobile U.K. contract is actually for using the T-Mobile U.K. GSM network (which it may or may not be), there is a good chance that a tri-band phone from the U.S. won't work on it at all.

There are two GSM bands used in North America -- 850 & 1900 MHz -- and two used in the U.K. and Europe -- 900 & 1800 MHz.  An American tri-band phone will usually have the two North American bands plus the 900MHz British/European band.   However the T-Mobile U.K. network uses 1800 MHz only, so would be inaccessible to such a phone.

Only two of the U.K. networks actually support phones using the 900MHz band, these being Telefonica/O2 and Vodafone, which are the two oldest networks (O2 started out as BT Cellnet).   

I had a T-mobile PAYG phone in the US. I brought it over here, popped in a free Orange PAYG SIM card, found out the phone's unlocking code online (just do a search for your brand/model), and everything worked fine! Like another poster said, though, if you don't want to bother there are plenty of cheap PAYG options in the UK.