To utilize services on the remote bluetooth device it is required to enter pincode of that device.
$ niko@niko:~$ btctl addpin default "1234"
This command adds default PIN code which will be used to connect to all devices.
As Nokia 7560 support Dial-up Networking service we can connect to it using connect command. First I added my laptop to list paired devices of my phone despite it is not necessary. If you have running btsrv small gtk application will ask for passcode, otherwise passcode is handled by addpin. Now we can connect to DUN service.
niko@niko:~$ btctl connect 1 DUN
Connecting to host 00:02:ee:46:22:39 ...
Service found on channel 1
Connecting to channel 1 ...
Connected. Bound to line 0 [/dev/bty0].
Now connection established and phone behaves like a modem on /dev/bty0. You only need to change device name in your ppp configuration files from /dev/ttySx to /dev/btyx.