Why reverse the details on the telephone?
If the telephone is not the router then it should have the same gateway and subnet mask (and SSID) as the PC with a different IP address (say 192.168.0.3). If you cannot set this then I would suggest that you leave the IP address for the PC left as auto.
If the telephone is your router then you will not need to set it's IP address as it holds the Gateway IP address.
If none of this answers your problems then some more information regarding exactly what your hardware setup is would help. Cheers