Looking at buying a pre-pay 5500

[lostplanetj]

I am looking at buying a 5500 to replace my ageing 5140i.

the phone i have my eye on is a pre-pay orange deal (where by i assume i will receive an orange boxed 5500 with sim card to be registered.)

i am an existing orange pre-pay customer but i would like to know what is the difference between a pre-pay and sim-free phones?

I would like to use my existing orange sim-card with tariff, contacts and credit already on it and i also have a vodafone sim card i would like to use in other orange signal poor places in the UK so it would be nice to have the vodafone option.

seeing that BB5 cannot be unlocked would you expect a pre-pay phone to be locked to the network supplier or cause other hassle?

next question is any owners of 5500 sport had problems with Ultra 2GB micro sd cards (sandisk)?

and can anyone recommend a decent pop-port to 3.5mm female adapter other than the AD-15 and AD-46?

thanks