Depending on where they were, they might have been beyond VHF radio coverage. We switch over to HF and Sat Com once we leave VHF (land based) coverage areas, when we go over the oceans and northern Canada/North Pole area to make our position reports. BUT...from what I've been hearing, Malaysian Airlines didn't pay for Sat Com, so their guys may have been using HF, and that is a huge pain in the buttocks, especially when you are on fire, and breathing in your 02 mask. The HF radios are complete crap, in terms of reception. Lots of static.

The LAST thing we do is make a radio call to report a problem, when it's a MAJOR problem, like a fire/depressurization, we are too busy to talk to ATC for the first 3-5 minutes. If we are already out of VHF range, most guys wouldn't even try to make an HF report. HF radios suck, and the coverage is terrible. You are not in radar contact by then, and the guy on the other end of the HF is probably fast asleep at 2am.

If their problem was an electrical one, it could have started with the electrical buss that powers the radios, rendering them inop anyway.