How does a 3G work?

Question

For the working of 3G is a sim card required is 3G dependednat on sim card via GPRS and is a Service like GPRS or is it independent like Wi-fi and would work even without a sim CArd?
Supposing I m using a phone with Wi-fi and 3G enabled but no sim card will i be able to utilise the high speed download of the 3G without simcard using Wi-FI ?

Thanks in Advance

Answer 1

3G requires AT&T Sim card in the US. You have to be in a area with 3G coverage and have a 3G capable data plan and SIM card. Phone also have to capable of 3G with the right frequencies