There are more variables than ever to consider when signing-up for cell phone service.

New shared plans offered by AT&T and Verizon are changing the economics of how individuals and families access voice, data and texting services. Additionally, as 4G phones become commonplace, understanding which carriers offer reliable 4G connections becomes all the more critical.

Before signing-up for a new cell phone plan for you or your family, chew over these five new rules for picking a cell phone carrier.

1) Determine whether a shared plan will save money for you and your family

Next month, AT&T is scheduled to debut its Mobile Share plan for new and existing subscribers. This follows Verizon’s Share Everything plan, which was introduced last month. Both plans offer unlimited voice and texting services for a fixed fee, and charge extra based on the number of devices included and how much overall data is consumed. While the pricing and services for each plan are generally similar, the biggest distinction is that AT&T gives its subscribers the option to choose between Mobile Share and other existing plans. New Verizon subscribers, however, have no other choice but to sign-up for Share Everything.

So how can you determine whether a shared plan is cost-effective versus individual plan options? Consumer Reports advises AT&T subscribers with “low or moderate” data needs to stick with individual plans as this point. Individuals with one smartphone connected to the Mobile Share share plan are charged $95/month plus taxes and penalties for 1GB of data. Overage fees thereafter are $15 for each GB. In comparison, individual voice and data plans on AT&T range between $59/month (450 minutes and 300MB of data) to $99/month (unlimited voice/texting and 3GB of data).

So the benefits of shared plans from both AT&T and Verizon only come into effect as you connect more devices (smartphones, feature phones, tablets, connected laptops) to your plan. Both AT&T and Verizon offer attractive packages that connect two smartphones with two feature phones and 4GB of data for $210. From there, the packages get more cost-effective as you add more devices and data to them.

While Sprint and T-Mobile also provide opt-in shared and family plans, their packages have not changed as dramatically in recent months. However, if AT&T and Verizon are successful with their new offerings, expect the two other major carriers to follow suit.

2) Monitor your data consumption – but don’t pay for more than you need

One additional and unfortunate wrinkle in Verizon’s Share Everything plan is that existing subscribers who enjoy grandfathered unlimited data plans will not be able to upgrade their phones at subsidized prices. That means that new and shiny smartphone you want to buy for $199 will actually run you more than $500. For most of us, that negates the benefits of having an unlimited data plan. Verizon is not the only carrier getting stingier with its data. Earlier this year, AT&T confirmed that subscribers still on their unlimited plans (no longer available to new customers) could see data speeds slow down after 3GB are consumed in a billing cycle. T-Mobile’s “Classic Unlimited Plan” for $95/month reduces high speed data after 5GB are consumed in a billing cycle. At this point, Sprint is the only remaining major U.S carrier to offer unlimited data plans.

But is not having access to unlimited data really the end of the world? According to Nielsen, the average smartphone owner consumes less than 500MB of data each month. So if you are a relatively light data user who likes to email, browse the web and maybe play the occasional game or two, you can save $10 to $50 per month or more on AT&T, Verizon and T-Mobile with plans that offer 1GB of data. Paying for unlimited data, or as much as 5GB of data per month, is best for family plans or individuals who constantly play games and/or watch videos on their smartphones without wireless Internet connections.

3) Research coverage maps for the best 4G networks in your area

As we increasingly treat our cell phones like handheld computers, the speed and reliability of the networks they are carried on become more important than ever. If you are about to purchase a new phone and things like high-speed Internet connections, video conferencing and HD gaming are important to you, than you should research which carrier in your area offers the best 4G connection. While AT&T is lauded by PCWorld and others as having the fastest 4G download speeds, the other carriers got a head start in offering nationwide 4G coverage. Before choosing a provider, check out the coverage maps offered online by Verizon, AT&T, Sprint and T-Mobile, as well as other regional providers you can access. You don’t want to shell out the big bucks for a state-of-the-art phone and two-year plan, and not have access to the fastest network possible.

4) Be mindful of your privacy before downloading certain applications

Advances in mobile media technology offer great benefits like the ability to identify nearby retail sales or happy hours in our area, as well as what our friends and contacts might be doing at any particular time. Of course, the counter-effect is that we sacrifice elements of our privacy to make these things possible. While many of us are proactive about deciding what personal information we are willing to give up for these services and conveniences, many third-party applications are not always forthright about what they are doing with our information.

Earlier this year, it was discovered that many popular apps like Path, Twitter and Yelp were uploading iPhone users’ address books to its servers without explicit permission. There is no evidence that the companies were doing anything nefarious with that information, and the offending app developers immediately revised their practices once they were revealed. Still, in this era where the technology is moving so quickly and so many new services are available at our fingertips, there is a good chance some of the information on our phones is stored by unknown third parties. Proceed with caution, and research the background and user and professional reviews of unknown applications before downloading them.

5) Consider a prepaid plan

While prepaid cell phone plans that don’t require two-year commitments have long been available, their biggest drawback was that they didn’t typically offer higher-end devices. This is no longer the case. Last month, prepaid plans for the iPhone debuted for the Cricket and Virgin Mobile USA networks. Those carriers and others are also beginning to offer among the best Android and Windows devices. There are still various pros and cons you should consider before investing in a prepaid plan. But if you resisted in the past because of poor handset selections, now is a great time to consider prepaid options.

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