A range booster/ extender would help. The wifi card in the PS3 is somewhat flaky and doesn't do as good a job with wireless play as one would like. It is true if the router is close to a cordless phone base it can interfere with the signal as both are using the 2.4 Ghz bandwidth.
Did you try setting up come custom settings in the router's DHCP for the PS3 and then putting all of the numbers in the PS3's connection setting manually (the IP you set up, router IP, subnet mask, DNS servers)? Doing that may help with getting your connection working.