There are millions of mobile phone users and there are some who never check their bills,I know because I used to carry out a job that enabled me to do so.
Did you know that this sophisticated system, that has been building into the monster it is today, has many billing faults,one of the prime faults is your telephone number.If like me you chose to retain your telephone number for whatever reason and you chose to change your supplier to another of the big four it is the original supplier whose tariffs are retained for people who decide to call you.
Let me explain a little clearer. My mobile was with Cellnet the name to changed to o2.I retained my number when the whole of BT (when I worked there)changed to Vodaphone.Therefore the tariff for calls made FROM my mobile was the Vodaphone tariff.But if somebody called me they would be paying on the o2 tariff (cross network calls)from their mobile.Now this does not sound too tragic. It only does when you realise that cross network calls (o2 to Vodaphone,Orange to o2 etc) are more expensive than if you were to call from the same supplier. Your supplier can tell you what was the original supplier of your number or you can find out by checking your bill. The discrepancy will become obvious when you compare costs for calls to what you believed to be a like tariff user and the costs are different to what you expected. It is very convenient toretain your number, but like a lot of hings you never get something for nohing.