Nomophobia is the fear of being out of mobile phone contact The term, an abbreviation for "no-mobile-phone phobia", was coined during a study by the UK Post Office into anxieties suffered by mobile phone users. The study found that nearly 53% of mobile phone users in Britain tend to be anxious when they "lose their mobile phone, run out of battery or credit, or have no network coverage". The study compared stress levels induced by the average case of nomophobia to be on-par with those of "wedding day jitters" and trips to the dentists. It is, however, arguable that the word 'phobia' is misused and that in the majority of cases it is only a normal anxiety.
It's a good job I don't suffer from it since my phone has been back to Vodaphone twice since I got it and both times it has had extended stays in their workshops. (The Moral - don't get nomophobia and don't buy from Vodaphone!)