MS Messenger cannot connect to the internet every time it tries to over the 3G connection
Yes, but, what's happening at the TCP/IP level? Failure to perform DNS resolution? Failure to find a route to the site? TCP connection attempt rejected (RST sent in response to SYN)? TCP connection attempt timed out (nothing sent in response to SYN)? Failure to negotiate SSL credentials? Or what?
And you still haven't given details of the ISP service you're connecting to. If you've bought the wrong sort of service you can end up in the network operator's walled garden with either no internet access or restricted internet access. Perhaps unlikely if some sites/applications work but not others, but it would still be helpful to know. So: What's the name of the service you've bought, and what's the Access Point Name?