Does the iPhone support pre-paid phone cards?

The better question would be does the company you want to get pre-paid cards from support the iPhone.

For example, in the US, AT&T will not. You may be able to get it to work for voice, but as soon as they realize you have an iPhone, they will cut you off. I believe T-Mobile works fine, but you can't use T-Mobile's 3G network in the US as it's not compatible.

Check with the carrier(s) you want to use. Technically, an unlocked iPhone 4 will work on any compatible GSM network, though not all functions will work depending on the network provider.

yes you can if its a pre-paid calling card your talking about ?

on the key pad dial the tol free number and loong press the * key

the , will appear and continue with your secret calling number followed by # key and save this number ,

dial this number from contact and wait for the voice instruction to compleate,

no, but you can but minutes along with your bill.

Depends on the carrier. Some carriers will let you activate a pre-paid sim with the iPhone, some won't. So, contact your carrier & ask.