I found this info about upgrading the firmware in a Linksys SPA-942 (and I assume SPA-94x) voip phone (www.tummy.com) WITHOUT USING WINDOWS:

You can upgrade the firmware by putting it on a TFTP server (which is what the windows updater does anyway!), and then in a web browser going to the URL:

http://<PHONE IP ADDRESS>/upgrade?tftp://<TFTP SERVER IP ADDRESS>/spa.bin

It may be possible to replace the tftp with http.