Oh it's even more fun than that. When GSM carriers went to 3G, they actually went to an air-interface called WCDMA (part of UMTS) - deployed in the US by AT&T and T-Mobile. There used to be giant flamewars over whether GSM or CDMA was the better technology. A few people are still carrying that old torch (like the OP). But the GSM snobs lost that war, and most of them don't even know it. Their beloved GSM carriers quietly switched them over to WCDMA technology for their precious 3G signals. Now, with LTE, everyone's playing with the same set of toys, with CDMA technology at the base of it.I talk and surf all the time.... LTE is GSM... Verizon supports VOLTE.... Internet search is your friend
And yeah, simultaneous talk and data work just fine on Verizon on my nearly two year old iPhone 6.