Yes you can, I have a iPhone 4 and I sent a iPod touch to Mexico, cuautla. And it work with no problem.
No you both have to have an iphone 4 :)
yes
No, there is although an iPhone case for the 4 that has a keyboard that plugs and you can use.
The iphone 4s desigh as same as iphone 4, so you needn't worry about that ,my girl friend's iphone 4s use my iphone 4 case (buy form 708buy.com) all the time, I prove the iphone 4 case is fit to 4s
No. It is not possible to use 2 apple ID's simultaneously on apple iPhone 4.
Yes I Use it every day it is my lock screen on my Mac and IPhone 4
Yes. They both use 30-pin docks.
The difference between the Iphone 4 and the iPod Touch is that the iPhone is techincally a iPod, but with phoning capabilities. Also, the iPhone 4 can use FaceTime, a app that use video calling. Also, the newest iPod has FaceTime too. So, both the iPhone and the iPod are both the same.
An iphone 4
Televisions that use the same LCD panels as an Iphone 4 will have similar display characteristics as an Iphone 4.
An iPhone 4 is an iPhone.....