Dell 5520 mini pci cellular card doesn't do 7.2 Mbps??

I have one of these 5520 mini pci cards fitted in my m1330 notebook. According to the specifications I have found this is supposed to support 7.2 Mbps coonections.

I have installed the generic dell broadband software from the m1330 downloads page; however it only ever connects to '3' mobile internet service at 3.6 Mbps and the performance is terrible. I know that '3' gives 7.2 Mbps service in my area because I can connect to it using an external dongle.

So how to I get the promised 7.2 MBps performance out of my internal Dell card?

Thank you

NigelS