I have an iPhone 4 with ios7 is there any possibility to revert back to ios6?

I Also want to jailbreak it so that I can use any SIM card in my phone, what iOS will my phone need to be on?

Don't listen to the other guy you will be wasting your time. Apple have stopped signing IOS 6 meaning it is impossible to downgrade from IOS 7. When you downgrade/upgrade iTunes says it is verifying to update to apple. This is basically asking Apple if you're allowed to install this firmware. As Apple have stopped signing IOS 6 they will say no and you will have countless errors and maybe even brick your phone. You will only have to wait till around January as they have all the parts for IOS 7 jailbreak but they're just putting them all together to make it happen.

There's no way to revert back to an earlier iOS version as Apple have stopped signing them.

You can need to wait for a new jailbreak to come out.

You can check here for genuine jailbreaks; http://www.isthereajailbreak.com/