I have a BB8520 and wanted to share my thoughts since I have been using this phone for over an year now.
I am on a limited blackberry internet service(BIS) plan, which has the following:
1) I can configure 10 email accounts for push messaging
2) Blackberry messenger
3) Yahoo/Google/MSN messengers
The service costs are 299 per month + Your regular post paid rentals and call charges.
The unlimited plans opens up everything which includes unlimited surfing, but then it costs 899 per month (way too expensive!)
The only thing different about this phone is, you all know it, the privilege to say this to someone "Please call me on my blackberry" :)
If you are not going to use a BIS plan on a BB then waste of money, there are thousands of better option available!.