Help Change SIM card query.

[npfiii]

Hi,
I'm currently on O2 in the UK (although my Z is factory unlocked), and I'm thinking about buying an AT&T GoPhone SIM card for my upcoming holiday to the US and have a few questions...

• Will my Sense account recognise the new SIM and allow my to 'see' the phone, and will i be able to sync my Google/Facebook/Twitter accounts?
• If I simply swap the SIM over, can I expect to see any features/apps unavailable to me?

• Will I be able to access my contacts (stored on the phone, not my O2 SIM)
• Will the APN info I've entered be automatically detected, or will I need to manually choose it? (obviously this is nothing major, but it would be nice if it happened automatically)

Apologies if these seem like stupid questions, but with dumbphones it was much simpler to swap SIMs over, whereas smartphones seem to have a lot more variables.