I'm not sure what's going on but recieved my iphone 4s this morning and ever since I moved my sim into it, the signal is very sporadic. It goes from full signal, down to 1 bar then no service (for about 3 mins) and then back up to full signal (with no 3G). It's been doing this for over 3 hours now. I only get signal for about 25 seconds and I can't make calls.... I have tested other sims and looks like I have a dud. I have my old iphone 4 running fine with another vodafone sim. I just can't get the 4S to work!