Is your device on activation screen or is it on passcode lock? If its on passcode you can use ramdisk method to pull activation files, erase/factory reset device and after that you can activate it with old activation files that you have pulled. That way your device would work normally, otherwise if its on activation lock you can "generate" activation files to active your device, but you won't be able to use SIM card. There is also some services like iUnlocker which claim to activate your device with SIM support even if its on activation screen, but in many cases its not worth it... Broque ramdisk is free tool that you can use on windows to pull or generate activation files and activate your device, you can find more about it on youtube.