I too used it in Mexico just a week ago on a Treo 750 - I used it all with WiFi at a hotel for several days, with a wired headset. Worked fairly well.

I also have a Dell 51v Axim, which I think worked better (used them back and forth), but the 750 certainly worked "good enough" with Skype, I could have been fine with it and nothing else.

Wired headset is a requirement, I just used the cheap "bud" kind that came with it, but they worked well.