Mobile phone question

I bought my son a phone from virgin mobile, on pay as you go. However, I want to change it to the liberty sim card from virgin - it's a better deal for him. My question is, how do I do it? Will the sim just work if I buy it, or do I need to unlock the phone, which I don't know how to do either.

Have looked at the website for half an hour and am even more confused.

If it's the same network then the new sim will work in that branded phone no problems (as far as I know, I haven't owned a virgin phone before, though). If it's a new sim with a better rate/deal or whatever, try calling virgin and asking to be switched to that scheme, then he can keep his number (although it appears you may have only just bought it so that wouldn't make any difference). I did that with Orange.

[ChrisCaveman]

Ok!

The sim card you have bought will be able to have the Liberty Sim package on it, no problem, so no need to buy a new sim.
In regards to the phone, if you have a phone that works with the PAYG sim, it will work once the package has been set up! If not, you would need to contact the supplier of that phone (Orange, 02, Carphone warehouse, wherever you got the phone from basically) to get the unlock codes. You may have to pay a fee for this as well.

Send me a PM with details (number, which liberty sim package you want) and when I get into work tomorrow, I'll call you back to set it up