I've used Skype on my home computer for over a year and I've gone without a landline since then (I have a dedicated Skype phone #.) I'm thinking of getting a mobile plan but I also like having the convenience of being able to check the web wherever I go (with Blackberry service.) So I'm considering getting my first Blackberry and installing Skype on it as an alternative, but I have a few concerns for anyone who has used this combination:

1) How is the call quality when using Skype on a Blackberry?
2) How much does the typical unlimited data plan run these days (in the US)? Would it be considerably more expensive than getting a mobile plan?
3) How is the service coverage for Blackberries? I might occasionally travel overseas and it would be best if I can use it there.