If I buy an iPad 2 that includes Verizon or AT&T service do I need a contract, and will this allow the iPad to be used as a cellphone?
The Verizon and AT&T plans for iPads are month-to-month deals, not long-term contracts. You can choose never to activate them, or to turn them on and off based on your needs. These plans are for data only, however. They don’t endow your iPad with cellular voice calling capability. More information is here.
What is the PC equivalent to a MacBook Air? I’m tempted to get an Air but virtually everything I have is on a PC.
There’s a new type of Windows laptop generically called an Ultrabook that’s aimed at emulating the MacBook Air’s speed, lightness and battery life. I haven’t reviewed them yet, so I can’t recommend one. But two examples are the Acer Aspire S series and the Lenovo IdeaPad U 300s.
Is the Siri on the iPhone 4S different from the Siri app I downloaded awhile back on my iPhone 4?
Apple bought Siri soon after the original small company launched that app. Apple decided to incorporate it into the phone’s base software. There are some differences, but the functionality is similar. However, the old Siri app is no longer available, and, if you have it, you can no longer connect to the servers that make it work.