'Internet' usage vs 'BES' usage

I've recently signed on to the 'corporate blackberry option' over here in the UK with T-Mobile. Upon doing so, I was informed that this option gave me 50MB of 'email usage' along with 3MB of 'internet usage'.

Now, I think of myself as pretty good when it comes to networking and how data is sent and as such, I am thinking that only way T-Mobile can differentiate between the above two items is by the port in which information is going out/in on or possibly the fact that information is being sent/received with the PIN attached to it.

So.....
A lot of programs allow you to specify the 'Transport' for your information. As an example, Jivetalk allows you to do this. Under the Advanced options, you can either select 'BES' or 'TCP'.

What I'm wondering is if anybody has played with this at all? I mean, if I specify the transport to be BES (I am running with an enterprise server and not a BIS, BTW), then am I utilizing the 50MB entitlement? If I specify 'TCP' am I using the 3MB entitlement?

Short of trying it out for a month (and potentially receiving a nice fat bill at the end of it all), I was wondering if anybody knew outright!?

Cheers!