I don't think VoIP is connected to Heartbleed, but as it becomes more widely used, there will be a lot more weak links to worry about - at least until both end users and enterprises step up their efforts to properly secure VoIP.
My latest article on this topic has been published now by U.K.-based Enterprise Management 360. I've been doing things with them for a while, and their current print edition is out now - Q1 2014. The magazine is big and glossy - very impressive looking - but they also have a digital edition. There are apps you can get from their website to download it to your mobile device, but the link to view it online isn't up yet.
Until then, I wanted to share my article, which is part of the Q1 2014 edition. The publisher has provided me with a PDF version, and I've web-enabled it so you can view it here. I hope you like it, and more importantly, I hope it gets you thinking more critically about the connection between VoIP and IT security.