Why do cell phones drop calls?

There is no techincal reason, it's just the company like T-MOBILE, i used to have it and it dropped my calls. Now i switched to Cingular Wireless. Ive had it for 2 years and they havent dropped a call on me. The phone does not drop calls. But after like 3 years, you should update and change phones. Get a Nokia. They last forever.