WorldIRC; try following these steps - with modifications to your speeds/phone to see if it helps. (I omited step one because it asks for providers gprs apn settings; I'm thinking if I posted it would be an insult).
2.????From the Apple menu, choose System Preferences.
3.????From the View menu, choose Network.
4.????Choose New Location from the Location pop-up menu.
5.????Type a name for the new location such as "Wireless Modem".
6.????Choose "Network Port Configurations" from the Show pop-up menu.
7.????Make sure the "USB Bluetooth Modem Adapter" is enabled. Deselect the ports or interfaces you aren't using in this location, such as "Built-in Ethernet", and "Internal Modem".
8.????Click Apply Now.
9.????Choose "USB Bluetooth Modem Adapter" from the Show pop-up menu.
10.????Click the TCP/IP tab, if necessary. Choose "Using PPP" from the configure pop-up menu, and enter the DNS numbers and search domains as provided by your mobile phone operator.
11.????Click the PPP tab, and enter the account name, password, and telephone number as provided by your mobile phone operator.
12.????Click PPP Options. A sheet appears. Click "Use TCP header compression" to disable this option, and click OK. Your operator may be able to tell you if you can leave this option turned on or not.
13.????Click the Bluetooth Modem tab, and choose a mobile phone model that closely resembles yours from the Modem pop-up menu. In some cases, your mobile phone operator may provide a specific modem script for you to use.
14.????Click Apply Now.
15.????From the View menu, choose Bluetooth.
16.????Click the Settings tab, and select "Show Bluetooth status in the menu bar" to enable that option, if necessary.
17.????Make your mobile phone "discoverable" to other Bluetooth devices, or turn on Bluetooth communication. See the documentation that came with your phone for instructions.
18.????Choose "Search for phones" from the Bluetooth menu bar item, and select your phone, which you have already paired.
19.????Once your phone and Mac are connected, open the Internet Connect application.
20.????Click connect. Your telephone should connect to your mobile phone operator, and in 10 to 20 seconds, you should be able to use the Internet.