anyone ever tried these higher gain antenna with the wrt-54g's for UMA?

A high gain antenna would work well because of the higher gain and both incoming and outgoing. I utilize CompUSA branded ones at one location and they seem to work just fine.

You can get different high gain antennas that range from 5 to 9dbi

confero24.com//index.php?cName=5dbi-7dbi-24-ghz-dipole

confero24.com//index.php?cName=8dbi-9dbi-10dbi-24-ghz-dipole

Consider also getting yourself a 3rd party firmware for your router (use with care!). I really like the firmware put out by dd-wrt. These firmwares are generally free for non-commercial use. Not only do they add a lot of features to your router, but you can also dial up the output on your antennae in some applications. Combined with high gain antennae, I've had great results. Don't dial up the output too high or you get errors. Search around the forums on dd-wrt.com for more info.

Added high gain antenna and also ran a cable from 2nd antenna connection from 2nd floor to basement with another antenna down there. Spreads the signal well.

I would like to know how much output power the phone is set to use at max. If you exceed that on the router, you would just make the UMA unstable since you'd have good incoming reception on the phone, but bad going the other way to the router.