Comment 3 for bug 1329945

AnandTech has comparison charts of how Android (2.2, at least) and iOS (4.0) map signal strength to bars.
<http://www.anandtech.com/show/3821/iphone-4-redux-analyzing-apples-ios-41-signal-fix>

I had assumed that if the signal is strong enough to connect to a carrier at all, it's strong enough for a phone call. Is that not the case? And if it isn't, do we know where the cutoff is?