Let's say that you are looking to find the least expensive cell phone service in America. For example, say you want to have a cell phone strictly for "emergency purposes", so you aren't going to use it much if at all on a month to month basis. Or let's say that you want to have a phone that you do not plan to use very much — say 20 or 30 minutes a month.

I've looked around, and as best I can tell I think that Virgin Mobile is the cheapest way to go. Virgin has a pay-as-you-go cell phone service. Here's how it works:

1. You have to buy a phone from Virgin. The cheapest one you can get right now is a Nokia phone available at Wal-Mart? for $19.
2. You have to buy a "top-up card" to put minutes on the phone (or you can use a credit card through the web site). The cheapest top-up card is $20, and you must top-up every 90 days even if you don't use the phone.
3. If you use the phone, you pay 25 cents per minute for the first 10 minutes every day, and then 10 cents per minute after that. There are no long-distance or roaming fees with Virgin.

For a zero-usage phone, you will be paying $20 every 90 days to keep your number active. If you use the phone for 20 minutes a month at the rate of a minute or two every other day, you'll pay 25 cents a minute, so you will actually use the $20 that you put on the phone. In other words, whether you use the phone for 0 minutes per month or 20 minutes per month, it costs the same.

If you assume that the phone lasts 24 months, and it costs $19, you are paying less than $1 per month for the phone. $20 divided by 3 months works out to $6.67 per month. So that means that it costs $7.30 per month for nationwide cell phone coverage in the United States using Virgin. You can use your phone 20 minutes a month for that amount.

It would make sense to use Virgin's service up to about one hour per month. After that, there are probably cheaper options.

If you are willing to spend more for the phone (about $90) you can get a camera phone. It costs a dime every time you send a photo.