I mean, basically every major mobile in the developed world adopted IPv6 when they were rolling out new core infrastructure to handle LTE (T-Mobile USA being notable as one of the first to go IPv6 only). When you consider the deployment of VoLTE (and now VoNR for 5G networks) in particular, rolling out IPv6 internally removes a lot of nastiness that SIP/IMS have with NAT (and CG-NAT in particular), so it's little surprise that it happened.
What surprises me more is the very mixed state of small to midsized ISPs. Sparklight (regional cable provider) still does not support IPv6 in any fashion even though it would be financially beneficial to auction off a significant portion of its v4 holdings (nearly 1.3mm addresses), deploy DNS64+NAT64 (plus CG-NAT as a fallback) and hold onto a chunk for their business customers who still need inbound v4 connectivity. My local fixed-wireless ISP that's my only real option (love them, but this is a bugbear of mine) since I moved last year only offers CG-NAT, and I know their equipment can handle v6 fine which would save them some resources (no expensive state tracking on edge equipment or dedicated CG-NAT gateways) and provide a better customer experience (multiplayer games, VoIP traffic, etc.)