Yesterday's observation: the activation process for 3 Mobile Broadband needs work.
I bought a USB 3G Modem plus prepaid recharge voucher from 3. I clearly remembered selecting Mobile Broadband and carefully following what was happening on the screen, but when the activation finally completed 24 hours later, I saw that it only showed recharge options for phone services.
I can guess what may have happened. I think the activation process is not based on the SIM. (It should be: they should have a record that SIM # foo is for data rather than phone.) Nor is it based on what I select on the screen. I reckon it's based on polling the device the SIM is in during the activation step. That makes it my fault: they did say to make sure the USB modem was in the computer, with the software installed and the SIM inserted. I didn't do that ('coz I didn't see the point – I just wanted to activate the service).
So why is it their usability problem? Because the design requires people to follow instructions that don't seem immediately relevant to activation and there is no explanation of why they are relevant.
It could be improved by appending the instruction: "Already set up your modem and your Internet Key Modem is plugged in" with something like "This will ensure 3 knows your SIM is for Mobile Broadband".
It could be improved further by tracking which SIMs are for data or for phone.
And lastly, I'm just one user, talking (way too verbosely) about one very minor thing. To improve usability properly requires further user observation.