check your hotels ONLINE. Or take one of those phone company gizmos (not sure what they are called) that plug into your computer and give you wifi access. Our villa had one and it worked great. Better make sure you get an AT&T one as that is the preferred network on STT.
If others have better info for you, good. BUt I did a lot of personal checking before I went there.

air card.

There are several locations where if you BUY something you can get WiFI for a periond of time.

but Free and STT probably do not exist at the same time.

billd

Someone asked the same question on another forum and were linked to a website map which showed free WiFi spots in at least Charlotte Amalie. I don't know how good it was but you could try googling, "St Thomas free WiFi" and see what comes up. I would do it myself but my Google is temporarily sick!

Magens Bay supposedly has free wi-fi. Wendy's had it at one time.

I'm sure there are quite a few unsecured wi-fi networks around the islands, but I doubt that there's a published, complete, accurate list. When I log on at home, I sometimes get notifications of several networks in my area, but only one seems to be reliable/accessible.

Betsy's Bar and The Looney Bien in Frenchtown both have free WiFi.
Jay