it sounds to me like the settings on your provider (mobistar) are not set properly for a data connection nor a blackberry internet service. I don't know how things work exactly with Mobistar or in Belgium so someone from there will have to answer as far as that goes.
the data connection refused and the lack of a browser both indicate that the device is not configured for a data connection, when it is properly set up, the browser will appear after the handheld is registered on the wireless network. the APN settings will apply after you get your internet/data plan activated on your account.
I assume that you are going to want a Blackberry Internet Service (BIS) account so you need to set that up before you are able to use the data features. I found this website that may help you: Mobistar
Also, as far as the text messaging, that is something that you may need to discuss with Mobistar as it sounds like it is something on their end that may be set incorrectly.
again, this is all how it works in the US, but I would imagine it is not too dissimilar where you are.. I would give Mobistar a call and make sure everything is set for BIS on their end..
Hope this helps!