Many times, randomly, people say that their calls go straight through to voicemail... I realize the iPhone does this while on the internet, but it happens sometimes when I'm not on the internet. My phone was sitting on my desk for a while, not doing anything, the person in the same room did a test call to my iPHone and it did not ring. 5 mins later, we tried again and it worked. This happens numerous times everyday. Any ideas?