Why do cell phones drop calls?

Ok, I've had this problem with all different companies. At first my new phones seem to work great but not long after it seems like they are always dropping calls. I don't think its necessarily the network because many times in the middle of my conversation my signal drops to nothing and my call ends and as soon as I close my flip and re-open I have 4 bars....seriously...WTF?!!! I even had one one company that was like clockwork....on long calls, just about every half hour my signal would drop off to nothing.

Is this a problem with my phone because of age or something else or is this something the phone companies do because their towers are overworked?

I'm really looking for a technical reason why, not guesses please.

Cell phones drop calls because they have to either modulate multiple calls on one based station, or hand-off the call between base stations as the caller travels around. The third issue is that signal strength may be low and the base station can't stay locked with the phone.

The way to minimize this is to:

Choose a provider that has maximum coverage in your area. There are coverage maps available on the Web. This is the most important since the investment made by the provider in base stations for coverage means the fewest dropped calls.

Second, research the phone you choose to buy to get one that has a good track record with the provider you choose.

Finally, if it's a critical call, stop your car so that you have the best chance of staying locked to the base station until you complete your call.

All in all, not great solutions. We are hoping that as the new cellular standards come on-line, and the FCC opens additional bandwidth via switching some analog TV broadcast spectrum to cellular, the situation will improve.

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.