in my previous job, we have deploy around 2000 wifi phone, and to resume, the most important aspect will be tthe choice of the client.
we test different wifiphone :
aastra 312, aastra 320 (hard made by unidata 7800), unidata 7700, cisco, and ascom i75 and the best that we test in August 2011 was the Ascom i62.
at this period i was in france, now in canada and i try to find some equivalent in the local market, but nothing yet.
the other big advise, if you can, use the 5 Ghz with a min level of 65 db in youre WLAN.
after you will have to calibrate youre architecture with the environement, perturbations, budget and others good things...
good luck:smileywink: