I bought web n walk for my paygo blackberry to get internet and the blackberry messenger still isn't working people arnt able to receive or even send me invites.the facebook and msn messenger for blackberry also doesn't work.is there a way of solving these problem?

I'm guessing that you don't have a blackberry data plan -- just a generic data plan. You need a Grade A, certified BlackBerry data plan.

Which is not available through most paygo providers.

Gotta have a BB data plan. No substitutes accepted and none will work for any RIM connected services such as BBM, email, and others.

Orange UK is the only carrier I know of that presently offers PayGo BlackBerry data service.

Correct.
Web n walk will NOT work with PAYG, on any BB.
To get the BB services on the PAYG tariff with t-mobile, you need to have bought their BB PAYG with BB services.
You cannot add BB services to a PAYG plan.