Cisco ATA 187

Looking for the standards that would help to improve Cisco ATA 187 signal quality by impedance setting... The closest settings for Switzerland, I could find by googling is this http://en.wikipedia.org/wiki/Two-wire_circuit 270Ω + ( 750Ω || 150 nF ) to be verified tomorrow... by default Cisco sets 600 Ohms complex which seems to be oriented to North American market.