I recently did a teardown to replace the home button on an iPhone 4. When I powered it back up and saw "No Service", my heart dropped. Fortunately, after reading this forum and others I went into field test mode (*3001#12345#*) where I noted that the statistics were last updated in 1969. After failing to change the date in iOS 7, I turned on WiFi and joined my home network. In seconds the date was updated and then the phone joined the GSM network with ease! Hope this helps others.