I have just started getting a couple of numbers not recognised yesterday, which I didn't think too much of as I thought there maybe a temporary network issue. My wife has recently had a replacement SIM card from O2 and worked fine when she installed it 2 days ago, but now it's not recognising that either. She calls me fine but I can't return her call. We have both restarted the phones but it's not resolved the issue. Any ideas?