Here's how to set configuration Opie Version 1.2.1 (Familiar Linux v0.8.4) installed on an HP IPAQ 3970, so you can connect to the internet via GPRS at any time...

as a first step activate the bluetooth on your phone and make sure it is not enabled the option that makes it invisible to all mobile devices that have not already established a connection authorized.
Enable ipaq bluetooth and proceed with the verification of the connection from the handheld to the phone by opening a console and typing the following command to determine the physical addresses of nearby Bluetooth devices:

hcitool scan

will produce a result like this:

Scanning ...

00:22:4B:11:61:BF johnphone

try to test the communication between the handheld and mobile phone with the following command:

l2ping 00:22:4B:11:61:BF

if the result of the command will look like this, the two devices communicate with each other properly:

0 bytes from 00:22:4B:11:61:BF id 0 time 55.30ms
0 bytes from 00:22:4B:11:61:BF id 1 time 41.61ms
0 bytes from 00:22:4B:11:61:BF id 2 time 30.13ms
0 bytes from 00:22:4B:11:61:BF id 3 time 28.83ms
0 bytes from 00:22:4B:11:61:BF id 4 time 36.20ms

At this point you must find the channel used by the phone for the service "Dial-Up Networking" with the command:

sdptool search DUN

in this case the result looks like this:

Searching for DUN on 00:22:4B:11:61:BF ...
Service Name: Dial-Up Networking
Service RecHandle: 0x10017
Service Class ID List:
"Dialup Networking" (0x1103)
Protocol Descriptor List:
"L2CAP" (0x0100)
"RFCOMM" (0x0003)
Channel: 3
Language Base Attr List:
code_ISO639: 0x454e
encoding: 0x6a
base_offset: 0x100
Profile Descriptor List:
"Dialup Networking" (0x1103)
Version: 0x0100

What interests us is to retrieve the channel number used by the service, in this case is 3.
Bind to the channel Dial-Up Networking service:

rfcomm bind 0 00:22:4B:11:61:BF 3

now we need to verify that the device was associated after bind to the channel performed correctly:

rfcomm show

if the result is something like this everything works fine:

rfcomm0: 00:22:4B:11:61:BF channel 3 closed

now you can try using the modem's GPRS mobile phone with the program minicom configured on the device /dev/rfcomm0 and trying to type some AT command to retrieve some information:

atz
ati
ati1
ati2
ati3

you can also try to directly call a phone number:

atdt023456**

All these operations can be automated by editing the file /etc/bluetooth/rfcomm.conf on the handheld, as follows:

#
# RFCOMM configuration file.
#
# $Id: rfcomm.conf,v 1.1 2002/10/07 05:58:18 maxk Exp $
#

rfcomm0 {
	# Automatically bind the device at startup
	bind yes;

	# Bluetooth address of the device
	device 00:22:4B:11:61:BF;

	# RFCOMM channel for the connection
	channel	3;

	# Description of the connection
	comment "Nokia N70";
}

in this way when enabling Bluetooth on your handheld, automatically will connect with the modem's GPRS mobile.
Now configure Opie to make a Dial-Up to Internet service provider, for example, for the telephone operator Omnitel is necessary to specify:

Phone Number: *99#
Str init modem 2: at+cgdcont=1,"IP","web.omnitel.it","",0,0

here are some screen shots captured directly from a Opie handheld where the configuration has been proven (Settings-> Network):