A good reference for this is to check out one of the EUTW servers (use filter in server browser.)
There is usually one of them at full capacity starting from late afternoon (GMT+1).
You can observe lagging voip in the following channels:
- Global channel
- Command channel
- Side channel
It will work fine for:
- Group channel
- Vehicle channel
- Direct communication
Please try to fix this for the next patch. As mentioned by lot of people, this kills teamplay on multiplayer servers.