I've been wanting to to do this for months and I finally had some free time yesterday. I added an external antenna connector to UTStarcom F1000G wireless SIP phone. http://www.skifactz.com/wifi/F1000G_antenna_1.htm

I connected the phone briefly to a conifer antenna and a biquad. I didn't have time to measure signal gain but I noticed that the phone was picking up more access points then with the built in antenna. I'll do some tests later.