There are an awful lot of disposable items in today's society--razors, diapers, cups, knives, and spoons. But who would have ever guessed that a mobile phone would, too, become disposable?
In reality, you wouldn't actually toss out a disposable phone after one phone call, as one might imagine from its name. Although disposable is not technically accurate, the idea is that these phones would serve in a diminished capacity from your primary phone. A so-called disposable phone is often ridiculously inexpensive (under $30) and comes with a SIM card of its own. This phone is as no-frills as it can get. It won't have bluetooth, video games, or a built-in camera. It is like having a mobile phone from the mid-1990s: it's just a plain-jane phone.
On the plus side, when you buy one there are no gimmicks. You don't have to sign up for any lengthy contracts. When you buy these pay as you go cell phones, meaning you only pay for the airtime you actually use. These were designed for people who are either afraid of commitment (to a phone plan contract), can't qualify for a contract due to bad credit or for other reasons, or someone who doesn't plan to use the phone for a very long time.
So what makes these phones disposable? Perhaps you have a friend from overseas visiting you? How do you keep in touch with her when you're not together? Pick up one of these nifty little phones and let her use it. You can often get free mobile-to-mobile calling if you purchase one on the same network as your existing primary phone. This way, you can keep in touch with your buddy for free.
Another idea is to use this phone as a backup to your primary phone. Let's assume you already have a nice $700+ smartphone, like a Nokia N96 or an Apple iPhone. You plan to go to a pool party, beach get together, or other aquatic festival. Nothing is worse than having your drunken friends or family scoop you up and toss you into the water without realizing they tossed a week's worth of your salary in there with you. So leave the expensive phone at home or in the car. Pop your SIM card into the cheapie, and enjoy your trip.
Are you on a blind date and not sure how it's going to turn out? Keep this spare phone (and phone number) for use with all any future dates you're not sure about. That way, if things don't work out, you can isolate all the undesirables to one handy, disposable phone number, thus avoiding embarrassing calls when you are out with your real friends. Using disposable phones couldn't get any more enjoyable!