User-Specific Timezones? Hack? Plugin?

Is there any way, whether it be a hack, a plugin, etc., to give users their own timezone? I am using a purchased SMS plugin. Users (my clients) login and are able to send out text messages when they choose. The plugin uses the post engine, including the scheduled post dialogue in the ‘Publish’ box, to send texts. Now, obviously the scheduled post dialogue works off the administrator’s timezone under ‘general’ settings, which is a headache when you have users around the world using the plugin. Is there any way to give users their own timezones?

There doesn’t seem to be much information about this on the WordPress site, except a ‘maybelater’ here or there. Is there any workaround, hack, anything that one can use to force user timezones?

Solutions Collecting From Web of "User-Specific Timezones? Hack? Plugin?"