But anyway, I have this "friend" who may or may not have lost a very expensive (at the time) 802.11g IP phone that ran windows mobile. Let's say, for the sake of argument, it was sometime around 2006.
And let's say that in 2012, he had a toddler that was jamming toys in the couch, and again in this hypothetical world, let's say that his wife was trying to clean the toys out of the couch and 6 YEARS LATER found this device. And it was still in good working order, only having been used for a few months before disappearing. But it had firmware from 2006 on it. And it was lost to the sands of time when Cisco bought Linksys. It's running one version up from the bone stock firmware, 1.00.06. Not 1.00.06A, mind you.
This is a story of that "friend", since clearly while being disorganized I'd never lose a $350 phone in my couch for 6 years, after all. That'd be embarassingly careless.
Aaaaanyway. Here's the story of how to upgrade it. You'll need an 802.11b or g access point. No, 802.11n won't work even though it should supposedly fall back to 802.11g. It won't until you get the new firmware on there, so forget it. Go to a coffeshop or something if you have to.
First, take it to version 1.00.06A (that A is important, it is crucial for the next steps. I found the web browser upgrade interface to be useful for nothing else than getting 1.00.06A on, anything but that tends to just make the web server error out and reset the connection.
This adds the ability to firmware upgrade from the handset directly. From there you need to get the wip330_sbe.bin file onto the handset. Once you have the upgrade from handset options, you're good to go. (You can get all these files, by the way, at http://psyduck.mudkips.net/~paul/wip330 and can use that url with your handset if you want, it's no skin off my back. Mind you, it's only 1.5m connection, but hey, at least you can get a copy. Linksys/Cisco don't host it anymore)
At this point you have a fancy windows ce .net machine, no sip phone, no nothing. But now, you can get to the new firmware release! YAY!
Once you have this, the on-handset upgrade can take you to wip330_v1_03_18S.bin, where you will have access to any network running open, WEP, or WPA1 (not WPA2!). If you are connecting to a WPA network and getting a prompt about WEP keys, make sure you have your authentication set to WPA/WPA2 (or WPA1/WPA2) PSK. It assumes WPA2 is WEP, no idea why. But it won't work. Mixed authentication mode will work okay, and leaves the more secure WPA2 mode available for other devices.