I have a iPhone 3GS. I never use voice and data at the same time. I pretty much never use voice. I will never take my phone to Europe. I hear that the charges for using data in Europe are brutal.
Verizon will allow you to use your iPhone as a Wi-Fi hotspot. That sounds great, but I wonder if that will be an additional fee. As I said earlier, the 3G network is not fast enough for a sole source of internet, but it would be nice when I am traveling.
Last time I was looking at phones, the Verizon plans were more expensive. My AT&T plan is $80/month (including taxes and other charges for unlimited data and 1500 text messages). I have another year left on my contract. I don't know what I will do when it ends. I like my iPhone more than the Androids at this moment. In a year, this could be different.