There are two basic rules:

1) If you get problems uninstall the version provided by your distribution and use the official git version.

2) If your phone was made recently (say year 2004 or later) use one of the following configurations:
Non-Nokia phones, using USB cable:

[global]
model = AT
connection = serial
port = /dev/ttyACM0 # check dmesg for the right name

Non-Nokia phones, using Bluetooth:

[global]
model = AT
connection = bluetooth
port = 00:11:22:33:44:55 # replace with the address of your phone

Nokia phones, using USB cable:

[global]
model = series40
connection = dku2libusb
port = 1

see gnokii wiki on how to set permissions to use this as non-root.

Non-Nokia phones, using Bluetooth:

[global]
model = series40
connection = bluetooth
port = 00:11:22:33:44:55 # replace with the address of your phone