Many AT&T iPhone subscribers are waiting with bated breath for Verizon Wireless to get the iPhone. But can these subscribers take their old iPhones with them to Verizon

In this week's Ask Maggie, I break the bad news to one AT&T subscriber that his wife will not be able to use his old iPhone 3GS on the Verizon network once the iPhone comes to that network. I also offer advice about selecting the best wireless carrier for you, as well as advice for selecting a new 4G wireless broadband operator.

Ask Maggie is a weekly advice column that answers readers' wireless and broadband questions. If you've got a question, please send me an e-mail at maggie dot reardon at cbs dot com. And please put "Ask Maggie" in the subject header.

Dear Maggie,

I am an AT&T customer with an iPhone 3GS. But I'm planning to ditch AT&T as soon as I can. I've heard that Verizon Wireless will be getting the iPhone in early 2011. I figure I'll get whatever new iPhone Verizon offers with the new service, but I want to give my old iPhone 3GS to my wife so she can use it on Verizo, too. Can I do this Also right now I have an unlimited data plan for my iPhone. Would I have to give that up if I switch to Verizon

Thanks,

Isaac

Dear Isaac,

As you've pointed out, Verizon Wireless is expected to get the iPhone early next year. Neither Apple nor Verizon has confirmed this, but several reputable news sources have cited sources that say a Verizon iPhone will be announced in early 2011.

Unfortunately, for you and millions of other existing iPhone customers, the current version of the iPhone will not be compatible with Verizon Wireless's network. AT&T and all the other wireless operators now offering the iPhone are GSM carriers. GSM phones have SIM cards that, in unlocked phones, can be swapped out so that people can use the same phone on different carrier networks that also support GSM. But Verizon's network uses a technology called CDMA, and it does not have a SIM card that allows unlocked phones to be used on other carrier networks.

So in your case, your existing iPhone 3GS can only be used on AT&T's network. You could unlock the phone and use it on another GSM carrier's network. T-Mobile USA is also a GSM carrier. And several carriers in Europe are also GSM. But there is another caveat to consider. T-Mobile and AT&T use different radio frequencies for 3G service here in the U.S., so even if you swap the SIM cards, your AT&T iPhone won't get 3G service on T-Mobile's network. Instead, it will only operate on T-Mobile's slower 2G/2.5G network.

As for your unlimited data plan, it's difficult to say what kind of plan Verizon Wireless will introduce when it announces its version of the iPhone. Currently, Verizon offers a $30 a month unlimited data plan for all smartphones. It also introduced a $15 a month plan that offers 150MB of data per month. Verizon executives have indicated that data plans might change so that customers are offered more options. But executives have also said they acknowledge that consumers like unlimited plans. So Verizon may decide to keep the unlimited plan, but they might ask new customers to pay more than $30 for it.

Meanwhile, AT&T has eliminated its $30 unlimited plan for all new smartphone subscribers. It offers a $25 a month plan that offers 2GB of data for the month. And a plan that costs $15 a month for 200MB of data for the month. If you had an unlimited data plan from AT&T that started before June 2010, then you can keep that plan as long as you like. But if you cancel your AT&T service or change your service to one of the tiered offerings, you cannot go back to the unlimited plan.

I hope this helps clarify the situation for you. There is still a lot we don't know about the upcoming Verizon iPhone, so stay tuned.

Dear Maggie,

My current AT&T cell phone contract is up and I'm looking for a new provider. I recently saw that AT&T ranked at the bottom of Consumer Reports' annual customer satisfaction survey. U.S. Telecom ranked No. 1. But I don't live anywhere where that service is available. What's the best way to find out who the best carrier is in my area

Thanks,

Marie

Dear Marie,

Choosing a cell phone carrier is a big decision. If you are getting a subsidized phone with your new service, you're likely signing a two-year contract, so you better make sure it works for you, since you'll have to live with it for at least the next couple of years.

You are correct, AT&T did not do well in this year's Consumer Reports' customer satisfaction poll. The group surveyed nearly 59,000 cell phone users in September 2010 and asked them various questions about their overall satisfaction with various cell phone services. AT&T was the only large carrier to do worse this year in the survey than the previous year. Consumer Reports said the company struggled in almost every category. And it ranked last among major wireless carriers in terms of overall customer satisfaction.

Consumers Reports offers a good overview of what you can expect from a service provider. But it doesn't tell the whole story.

Service quality varies greatly depending on several variables, including where you live and where you plan to use your phone. For example, AT&T may have gotten low marks among consumers nationwide, but the service works great in Delaware where my family lives. In fact, my father reports that he is able to make phone calls from his boat in the Delaware Bay, while my uncle who has a Verizon Wireless cell phone cannot.

Even within cities, cellular performance can vary. For example, I own an AT&T iPhone. It works great for me in my apartment, but my friend who lives just a few blocks east of me says that she can't make a phone call on her iPhone in her apartment without it dropping the call at least once.

The first thing I tell people when they are considering switching service providers is to ask their friends, coworkers, neighbors and family members about their own experiences. If you ask people who use phones and services in the same places you plan to use your new phone and service, you're more likely to get an accurate view of what your experience might be.

To get a basic idea of which carriers offer better coverage and service quality in particular areas, check out CNET's online cell phone service mapping system, enabled by Root Wireless. This tool compares voice and data service among major carriers in various cities around the country. Data for most cities is available in the tool, and Root is still populating its database with information for smaller communities and cities.

Users can share information about coverage, which can help improve the accuracy of the database and mapping tool. The graphical interface of the map lets consumers see where gaps in service may be.

But remember that coverage and signal strength aren't everything. Network congestion can degrade quality. So it's very important to talk to other cell phone users about their own experiences.

And finally, most major cell phone operators offer a 30 day guarantee. If you are not satisfied with the phone or the service you've just purchased, you can cancel that service with no penalty within 30 days of the purchase. So take advantage of those grace periods to put your phone and the service to the test.

Dear Maggie,

Is Sprint going to upgrade its 4G speeds to compete with Verizon's 4G network I've been using the Sprint/Clearwire service, and I've sometimes gotten speeds faster than 14Mbps, but I am not able to get those speeds inside my house. I'll stick with Sprint/Clearwire if they plan to upgrade the network to meet Verizon's speeds, but otherwise I'll switch to Verizon. I really want some fast speeds in my home. Please help me. I want to know who to choose.

Thanks for all the help!

Greg

Dear Greg,

Today, Clearwire customers can expect average download speeds of between 3Mbps and 6Mbps with bursts over 10Mbps. Verizon Wireless's new 4G service offers average download speeds between 6Mbps and 12Mbps. Edward Baig of USA Today wrote in his review of the new Verizon 4G service that he was able to get bursts of download speeds up to 23Mbps.

So based on speed alone, there's no question that Verizon's service is much faster than the one offered by Sprint and Clearwire. That said, the Sprint/Clearwire 4G service offers unlimited downloads and uploads. Clearwire offers a 4G-only service for $45 a month. Sprint offers a 3G/4G service with unlimited 4G service for $60 a month. (Sprint also offers an unlimited 4G only service for $50 a month.)

Verizon charges $50 a month for 5GB of data and $80 a month for a 10GB service. For every 1GB over those limits the company charges $10.

Depending on how much you use the service and how much data you expect to consume each month, the Sprint/Clearwire service may offer a better value even though the speed might not be as fast. It is much faster than most 3G networks, which offer average downloads 600Kbps and 1.9Mbps.

For more information about high-speed wireless data services offered by all four major U.S. wireless carriers check out this FAQ published last week. It gives a full description of services by each wireless carrier. And whether the service is considered 4G or 3G is offers a chart that compares the pricing and speed of each service.

If you have a question or comment for Marguerite Reardon, you can submit it here. However, because our editors and writers receive hundreds of requests, we cannot tell you when you may receive a response.

Submit your question or comment here: 0 of 1500 characters

Marguerite Reardon has been a CNET News reporter since 2004, covering cell phone services, broadband, citywide Wi-Fi, the Net neutrality debate, as well as the ongoing consolidation of the phone companies.