Unscrambling the networks
Q: What's the difference between CDMA and AMPS? And should both be together in a phone? Can I send a message around the world to GSM phones using a CDMA phone?
--Joao

A: Let's start with the first half of the question. Here in the United States, we use CDMA (Code Division Multiple Access) and AMPS (Advanced Mobile Phone System), among other networks. In short, CDMA is a digital network; in the most basic terms possible, calls should come through pretty clear. But AMPS is an analog network, where calls aren't always so clear. AMPS was the cellular network in use before the all-digital CDMA, TDMA, and GSM networks were deployed. For the most part, AMPS networks are still available, especially in rural areas, although you'll pay dearly when making an analog roaming call off a digital network. As for CDMA, a few carriers support this network, the big players being Verizon Wireless and Sprint PCS.

I typically prefer a CDMA phone that supports AMPS, simply because it means more coverage. When I need to make a call, I can't be bothered looking for a network or driving an extra 10 miles to find one. For example, if I'm stranded on the highway without a call box in sight and a phone that can't get any service, an analog signal (AMPS network) is usually available, and I can use it to make a call if my mobile also supports AMPS.

Finally, text messaging: In general, the answer is yes, you can send a text message from a CDMA to a GSM phone anywhere. However, your best bet is to check with the carrier first; be sure to ask about text messaging plans so that you don't end up with a devastating bill.

Deck of cards
Q: Where I can get my T-Mobile phone activated so that I can purchase phone cards from local department stores such as Target?
--Marilyn

A: You can go to T-Mobile and ask a rep to unlock your cell phone's SIM; this tiny card is typically hidden beneath the mobile's battery and stores all your service information and even some phone numbers. The procedure could cost up to $25, but it's probably not going to help you much. In order to use the phone, you'll still need a prepaid SIM card, not a prepaid calling card.

All in the family
Q: I need to get three phones for my family, and I'm not really satisfied with my T-Mobile coverage or a recent billing mistake I incurred. Where's the best place to see maps of the coverage area? Should I go from store to store or just check it online?
--Tom

A: Coverage maps aren't always accurate, whether they're online or in a store. You probably know all too well that a map can show the local area as having coverage, but as soon as you get the phone home, you can't get any service. Somehow, you discover you live in a dead zone and can't predict the future, let alone what service will work in your house.

What to do? Start by talking to neighbors and coworkers; ask them what service they use and how well it works. When you narrow it down to two carriers--trust me, this won't be difficult--head to the store, get the details on the return plan (typically 14 days), and try it out for yourself.

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