Bring over OLD mobile phone??

I will have to cancel my 2yr agreement I have with Cingular/AT&T in a couple months when I move but I was planning on setting up a plan there using the phone I have now.  Is this possible?  How do you go about setting up a mobile service plan?  Is it required to buy a phone with the service? 
Did anyone transfer service?  Possible?
Thanks!

If it has a SIM card slot and is quad band (tri band would work, but quad-band would be best, see one of Paul's threads on the topic) then it should be fine. I have a UK SIM card and a US SIM card and I switch back and forth between the two depending on which country I'm in.

You would have to get the phone unlocked, but there are loads of places around that do that and Cingular will even do it for you themselves if you have had the phone for a certain amount of time.

If you have an un-locked GSM phone that operates in either the 900 or 1800 MHz bands (or pref. both) you can just buy a SIM card and pop it in your phone.

If the phone works on both bands then any network will be fine, if only one you'll need to make sure the network supports that band.

Pay-as-you-go SIMs (pre-paid) are very cheap, somewhere between free and £5 depending on type, network etc.

You don't need to buy a phone to get service.

If you want a contract instead of PAYG you can get some without a 'free' phone but the price difference isn't much in my experience - but if you shop around you may get a bargain.

I see I see...  I do have this quad-band mobile with a SIM card, as I made sure when I signed the 2yr agreement.  Here in the states it is pretty expensive to get a plan without signing a lease to get you going (at least from what I have found in Houston).  I suppose it is easier to shop around for a pre-paid SIM in UK. 
Is there anyone that has transfered service?  I know there is T.mobile here and there so why not?

I bought a pay as you go SIM card from Virgin. I bought it right off of Amazon.co.uk. The card was delivered to my boyfriend's parents house the next day and I just had to call up and activate. I know I have heard of some people having difficulty getting a phone contract off the bat.

Is there anyone that has transfered service?  I know there is T.mobile here and there so why not?

T Mobile in the USA is a 'different' company to T Mobile in the UK - the two don't share anything.

Also, is your handset a Quad band PDA by any chance? if so, and if you use it to connect to the internet for email etc - I 'think' your may be using the EVDO standard. I think that standard isn't used in the UK. Just a heads up - I'm trying to get a more definitive answer myself on various handsets/devices in the USA to see if the EVDO system can work here or not.
If so, it maybe worthwhile to sell off your handset in the USA and use the money towards a UK certified handset to work with the UK equivalent standard of HSDPA.
Discount the above if you don't use those features!

Cheers, DtM! West London & Slough UK!

If the phone works on both bands then any network will be fine, if only one you'll need to make sure the network supports that band.

Vodafone and O2 are GSM900/1800.  All the other GSM networks are 1800MHz only.

I went the easy pay-as-you-go route.  I was in and out of The Carphone Warehouse in 10 minutes with a phone and sim card and paid about 30.  It's great not being in a contract!

I went the easy pay-as-you-go route.  I was in and out of The Carphone Warehouse in 10 minutes with a phone and sim card and paid about 30.  It's great not being in a contract!

I did the pay-as-you-go route as well.   

I went the easy pay-as-you-go route.  I was in and out of The Carphone Warehouse in 10 minutes with a phone and sim card and paid about 30.  It's great not being in a contract!

It's great being on a contract!
You talk and text and send picture messages and check your email and all you want, as many times as you want, for as long as you want and you never have to worry about running out of credit!

It's great being on a contract!
You talk and text and send picture messages and check your email and all you want, as many times as you want, for as long as you want and you never have to worry about running out of credit!

Very true, and I'm sure I will go that route when I'm more established, but seeing as I can count my UK friends on one hand, this has been a good way to go as a new person to the country.  But if I tried to do pay as you go back home with as many calls and texts as I got there I would have gone bankrupt!!!   Once I find a social life I'll commit!