As I said, it wasn't a network issue.
Actually, it was a network issue with the original iPhone, as GSM 2G doesn't pause data for an incoming call.
While the current Verizon CDMA setup doesn't have simultanous voice + data, this is also its strength, as an overload on one does not affect the other as it can and does with AT&T's 3G.
This is partly why CDMA users don't miss it too much (I'm sure some do), because it also means that they've always had reliable voice or data connections, which is important to many.