How easy is it to configure my UIQ smartphone to function as an emergency modem for my PC?

You'll need to keep your wits about you, but there's no reason why you can't do this fairly easily. First of all, make sure your smartphone can get online properly, by checking your email or surfing to a web page.

1. Get hold of a USB Bluetooth adaptor for your PC and get it working.
2. Pair up your P910 (or P900 or P800 or similar) to your PC in the normal Bluetooth way. Note that there will be a new entry for your P910 under Windows' 'Control Panel' 'Phone and Modem Options', e.g. 'Standard Modem over Bluetooth #3”, or similar.
3. Now go into Windows' 'Network Connections' and use the 'New Connection Wizard', proceeding as if manually setting up any other dial-up ISP link.
4. Pick your Bluetooth modem from the list and use “*99***1#” as the dial string. The '1' is the GPRS connection profile within the smartphone. If you're not sure that yours is '1', go into Windows 'Control Panel' 'Phone and Modem Options', select the modem and choose 'Properties', then 'Diagnostics' and 'Query Modem'. Scroll down the list of results from your P910 and you should see '+CGDCONT:1,”IP”,”internet”', or similar. The number after the colon is the one you want.
5. For username and password, use the same ones as set up in your P910 for its own Internet use.

That's it!