When you're buying a PDA phone, you have to shop for both the gadget and the phone plan. You're likely to use more data on a PDA phone than a smaller smartphone because the larger screen makes Web browsing more appealing and a keyboard makes it easier to answer email. You'll probably find you make more calls as well, because you're seeing more things that you want to talk to people about. Don't expect to save on text messages by using IM either; UK mobile network 3 finds that most users send as much text because they're sending IMs to the people they couldn't reach before. Windows Live Maps, Google Local and other handy online tools will use up a small monthly data allowance quickly, so look for either an unlimited data plan or a plan where extra megabytes of throughput aren't prohibitively expensive. Some plans also give you access to Wi-Fi hotspots free or at reduced cost; that can save money when you're surfing the Web from a coffee shop and some hotspots will also allow you to make VOIP calls.

PDA phones aren't subsidized as much by the mobile operators as standard phones are even though the manufacturing costs aren't that much more, and you'll pay a different price depending on which contract you take. A 24-month contact halves the price of some Blackberry models on Cingular, for example, in the UK. You can buy an unlocked PDA phone without a contract and use it with any of the networks, but you'll pay full price for that. With many U.S. operators, you get a discount for signing up online, but take the time to try out the models you're interested in because the operating systems, input devices and screens vary significantly between different models. Make sure you get a device you want to use as a PDA and a phone so you don't end up carrying two devices and paying for two separate phone plans.