Seriously considering an iPhone need some help

I am on a recent 18 month contract with t.mobile on the android HTC Hero, but i want to trade it in for an iPhone 3GS. What i need to know is:

if i buy an unlocked iphone can i then simply put my current t.mobile contract SIM in the unblocked iphone and have it work?

or is there an easier rout around all this that i don't know about?

thats the most important questions out the way.

but also heres another one:

are there any caveats that come with having a unlocked iphone? i've done some research (how accurate or honest they are i am not sure) that say things like:

"Important: You must connect the iPhone to a computer each time you switch it on after being powered off. This applies to all unlocked new iPhones. Straight-forward instructions are provided."

"Restoring or updating the iPhone will cause it to lock to O2. Current firmware on iPhone: 3.1.2."

"THE PHONE IS UNLOCKED BUT AS EVERYBODY

KNOWS THAT 3GS IPHONE IS LOCKED AGAIN IF ITS TURN OFF - AND THERE IS A SOFTWARE TO UNLOCK IT AGAIN WHICH COMES WITH THE PHONE"

Is there a specific type of unlocked iphone i would need to buy to avoid these caveats? like a "factory unlocked iphone" or something?

Is the T mobile a GSM SIM card, if so u may not need to unlock the iPhone. Got my 3G iPh in July 08 and just swapped in the SIM from Nokia and registered it thru iTunes and still operate without a Data Plan, and iPhone remains locked.

Thanks. How do I find find out if i have a GSM sim card?

popper said:

Thanks. How do I find find out if i have a GSM sim card?

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It sounds like your in UK? Correct me If I'm wrong but I think O2 and the other carriers of the iPhone in the UK, will permanently unlock your iphone for you for a fee, Once it's been officially carrier unlocked (Which is the best most reliable method) It will stay unlocked forever, simply insert your Tmobile sim card and you are good to go.

* Since were discussing Official carrier unlocking this topic should not be closed*

popper said:

"Important: You must connect the iPhone to a computer each time you switch it on after being powered off. This applies to all unlocked new iPhones. Straight-forward instructions are provided."

Click to expand...

I have not found this to be true.

"Restoring or updating the iPhone will cause it to lock to O2. Current firmware on iPhone: 3.1.2."

Click to expand...

Yes, restoring or updating the software on a non-carrier unlocked iPhone will re-lock it.

Is there a specific type of unlocked iphone i would need to buy to avoid these caveats? like a "factory unlocked iphone" or something?

Click to expand...

Factory/carrier unlocked is the best option for international travellers.

Thanks for the replies, i think i'm starting to get an idea. Factory unlocked is the way i need to go, and your right bargsbeer, 02 do in fact unlock for a small fee. but they only do so if you purchased the phone from an 02 store or car-phone-warehouse. So unless i buy a iphone from 02 and then get it unlocked its not any good to me.

So i have two options:

1. buy directly from 02 on pay as you go, then get them to unlock it, then put my t.mobile contact SIM in the iphone
2. buy a factory unlocked iphone off ebay and put my Sim in it.

what would you guys recommend for a less drama approach?

heres my last question, a silly one but need assuring. although these factory unlocks take all SIMs how will they handle a contract package deal that i currently have? like my minutes, text, unlimited internet? i keep thinking they will only handle pay as go sims only.

popper where did u get a htc hero on tmo

From t.mobile. I just called them up and sorted it out over the phone.