Increase Maximum Port Speed ?

I have installed a Bluetooth DUN connection in my deskop with my Nokia N73 cellphone using a Mni USB Bluetooth Dongle. Now when i'm configuring the Bluetooth DUN modem settings in "Phone and Modem Options" inside Control Panel, i can set Maximum Port speed upto 115.2Kbps(115200) only. But when i configure the modem settings under the General tab of the Network Connections Properties, i can set the maximum speed upto 921.6 Kbps (921600). How can i increase the maximum port speed in the Phone and Modem settings from 115 Kbps to 460.8 Kbps as my Mobile internet provider has the maximum internet speed of 245 Kbps ?
Professional SP3
My Operating System is Windows XP

1: go to control panel
2: go in network connections
3: double click on bluetooth DUN connection
4: click on properties
5: and change your speed from 115.2Kbps(115200) to 921.6 Kbps (921600)
6: you will get a speed of 30kbps or 40kbps of speed