With my Linksys WRT54GS router, that's just about the same usuable range I get. I also have the Netgear WGT628v2 (Super G) and get closer to 50 foot before the signal gets too bad to use. I have a pretty typically constucted house.
WLANs are suseptable to lots of environmental influences. Things you can't see in your walls and floors can have a major impact on range. Heating and A/C ductwork, copper water pipes, electrical cable for example. You might try moving the WAP around to various places to see what the effect is. Sometimes 8-10 ft "to the left" can make a lot of difference. It also helps not to use 2.4 GHz wireless phones at the same time like you mentioned. (I use 900 MHz ones without any problems that I can tell.)
Other obvious stuff, but I'll say it anyway: try to not put the WAP on or next to a metal filing cabinet, bookcase, PC case, etc. Try to make sure that there are no large metal object like refrigerators in the line of site between the WAP and the wireless clients.
Oh, and welcome to the forum.