IOS 7 Problem on my iPhone 4S?

I became impatient and downloaded iOS 7 on my iPhone with the help of a very tech-savvy friend, who somehow faked a developer account by paying something like $7.99 online. This was about a month ago, and everything has been working flawlessly so far. Just today, out of no where, my iPhone made a weird restart and said that I had to activate my iphone by signing into my Apple ID. However after many attempts to sign in on both my phone and connected to itunes, I was unable to continue after I typed it in.So, I restored my phone using iCloud hoping to just go back to iOS 6 but even after I restarted it, its giving me the exact same problems. Is there anything I can do? Perhaps a software that could force install iOS 6? Please help!

Your friend must not have knew what he was doing…
I myself actually put iOS 7 on a iPhone 5, and never
ever paid anything at all. But there is one mistake
that most people always do, which is not backup,
then restore the phone before installing iOS 7.
If you do as I instructed, then you will never have to
pay for iOS 7, and get all the updates via iDevice
for free all the way up to the final release.
Show your friend this whole post,

Put the phone in DFU mode and plug it up to iTunes to
restore, then go about installing iOS 7
Extra below

It looks like the UDID registration your friend purchased expired earlier than expected. You need to have your device's UDID registered again. I registered on for only $5 instead of $8, and they told me it was guaranteed to last for all betas of iOS 7.