My daughter broke her 3G a few months ago so I gave her my I phone 4. I upgraded to the 4S at the time. I like that it appears faster then the Iphone 4 and it says it is running 4G (I doubt it is) but the hype about Siri and being able to talk to it to have it do things I don't get. I asked it maybe two questions and have not thought about it since.
Same Charger and program used thought entire product line
Upgrading to a new phone transparent it just changes everything to the new phone
Lots of support can be found on line and off line
If you do not already have an Iphone then look between the Droids and Iphone
Which carrier do you use? On ATT Iphone work Great but on Verizon I have heard of problems with them.