Couple of things here:
1) Read the forums, every single one of your questions has been answered already many times over - heck most of them are answered within the stickies so you don't even have to go searching.
2) If your 12 then you won't be able to buy one yourself, as you can only buy an iPhone on a card..no cash etc..so keep in mind you will need an older sibling/friend or parent to buy it for you.
I'm going to answer your questions briefly anyway, but really - go and read the stickies in each iphone forum.
if i unlock it can i still sync with itunes and use that as my main music app?
Yes, it will work exactly like a locked o2 iPhone, just on a decent network
You can still sync it with iTunes/outlook..itunes just sees it as an iPhone.
Use Pwnage - there is a sticky with full instructions in the hacking forum. Stay away from Ziphone (which some people still reccomend), it is risky and has a high probability of bricking your phone. Just don't do it.
and will it void my warrenty
Yes and no - UK law means that any hardware faults have to be covered by the warranty, so if you screen or battery dies apple will fix it for you. However, if you break the software (ie brick it) they will not. You will also need to 'Virginise' your iPhone before taking it in for repair - by this I mean de-activate it and return it to the state it was in when you bought it. Pwnage can do this for you.
and say if something goes rong with it can i take it back
See above
adn how do i top up with it
theres no physical keyboard when you are in a phone call
so i cant use a voucher
You topup the same way as with any pre-pay phone...there is a keyboard when you are in a call, it is just not there by default..there is an option to show it when you are in a call.
-jake
EDIT: i dont want to jailbreak the iphone i like the iphone OS and want to keep all the apps that come with it
i also want full support with all of the apps
and i dont want to instal installer
Jailbreaking just gives you the OPTION to install 3rd party applications, it does not remove or replace any functionality on your phone, and you keep all the apple standard applications and interface. You don't have to jailbreak it to unlock but it is really reccomended as you can make so many improvements to the phone without any negative side effects.
i also want to be able to update the firmware with no problems through itunes
so basically i want a normal iphone but just on a different network
You can do this - but you need to be careful. Do not install any firmware updates without checking the internet to see what sort of problems it can cause. Most of the time it is safe enough to do, but you would need virginise your phone again before installing the update, and then re-unlock/jailbreak the phone afterwards..should be perfectly safe if you do that.
