You can hacktivate on iOS 4 through 6 on the iPhone 4, but not on iOS 7. OTA updating has not yet been introduced on iOS 4, and skipping 2 entire iOS thresholds with iTunes's update feature is not advisable. If you have complete SHSH blobs and APTickets saved previously for iOS 5 or 6, you can use them to restore to one of those iOS that you have blobs for. If you do not have blobs previously saved, you're either stuck on your current iOS, or, you'll need to borrow a SIM card from someone of the same carrier as your iPhone 4, use it to activate, then return the SIM to the lender
Sent from my iPad using Tapa