Definitely Motorola Droid
The Nokia E71 phone offers either 3G network. QWERTY keyboard, WiFi, USB port, and memory card slot. It is Bluetooth enabled, has GPS, FM Radio, voice dialing, a 3 megapixel camera and video capture.
Yes, you have instant messaging, plenty of available applications, very good WiFi, and the charge lasts for 12 hours. It has a qwerty keyboard and is very easy to type. The track pad isn't very sensitive, but as good as it needs to be. The camera is only 2 megapixels. It is a very good phone for it's price, and a cheap alternative to a blackberry.
There are a lot of useful features on a Blackberry smartphone. Here are some of them: Display, camera and video recording, GPS, wifi, internet access, maps, organizer, phone, social networking, touch screen, QWERTY keyboard and more.
KU990i doesn't have Wi-Fi but theoretically it is possible to make it have as well as you can have it on your graphical calculator. First you must have a cable to connect your KU990i to USB Wi-Fi adapter. Then you just write drivers for it. The main problem is, which language you should use. Best way is to make customized version of firmware and integrate the driver into the code. I don't know how is it possible, but here is a simplified guide; the way to do it, not how to do it.
The AT&T 8525 has integrated Bluetooth 2.0, WiFi, and more. It supports AT&T's music, video, and location based services. It also has push e-mail capabilities, a 2 megapixel camera, a QWERTY keyboard, and good call quality.
Android
A wifi phone is just a phone that can use wifi. You would connect it to a wifi network to get a better signal for faster web browsing than a cell tower.
A WiFi VoIP phone is a good alternative to a mobile phone because you can ring countries around the world for less. This makes international and long distance calls more cost efficient.
If your phone is wifi capable, yes.
you don't wifi is already in the phone
A prepay phone can connect to a wifi signal as long as it has a wifi receiver and there is an available wifi network within close proximity to the phone.