Hi basf,
Forget about data plan and service books from Vivacell. They have not heard about Blackberry phones
Once I needed even to spell it for them.
To surf Web via GPRS without data plan you need 2 things.
1) Go to Options-> Advanced Options -> TCP and fill inet.vivacell.am for APN. Leave the username and password blank.
2) Install Opera mini. (I use 3.1.8295 version)
On the safe side check that the data services are enabled. For that go to
Options -> Network -> Data Services (should be ON).
That's it. Run the Opera mini and it will setup up itself (when it starts first time should run tests for network settings) and you will be able to surf web.
Let me know if any problem occurs.