In fact I think this is not only an indication of VoIP, although it probably was in this case. I think incumbent operators in various countries tend to alter (or completely remove) the calling number from the signaling, as practcally nobody validates that number in order to route the call. It's my understanding that the reason behind this tactic is to avoid paying the agreed upon fees from sending international calls to each other.
For example if country A wants to send calls to country C it can opt to send them via country B if the economics favor it. I imagine this is probably illegal -- if indeed it is still going on -- since it probably violates agreements in place but that whole accounting system is unstable anyway. Most operators know this and will block calls without A-numbers but there are always ways around that too if you're not too honest.
In the end it seems that all "distance" must become irrelevant in the pricing schemes, as it is more and more difficult to separate local not only from long distance but from international too. On the other hand isn't it precisely this flattening of the cost vs distance curve that, at least in the short term, drives a lot of VoIP offerings?
Maybe the only solution to that problem -- if it is a problem -- is to regulate that every communication device (hard or soft) must have a GPS chip which will relate its location to the operator (regardless if the operator is VoIP, CLEC, ILEC, Wireless or whatever), so that location based billing structures can stay in place. Now _that_ would be a crazy idea wouldn't it?