and do you have to pay for service from a cell phone company for the voice calls?

When you pay for cellular service, you get a SIM card, which contains everything the phone needs for connecting to the cellular provider's network.

https://en.wikipedia.org/wiki/SIM_card

If we ignore prepaid options it really is identical to your current bundle of phone contract plus smartphone loan - minus the loan. You sign the contract, get sent a SIM card and pop it in the phone you bought elsewhere and off you go.

yes, pre-paid or plan.

prepaid = go to quick-e-mart and by recharge/credit when needed. plan = set up payment details through web portal or over the phone.

Actually in Europe for example, most prepaid sim cards also offer setting details through a web portal, and it just automatically takes money off your card on a set date in a month to recharge the SIM.