A valid response is that as soon as a data service uplink is provided, then common IP routing via the GGSN could take over, and everyone could be using messenge

A valid response is that as soon as a data service uplink is provided, then common IP routing via the GGSN could take over, and everyone could be using messenger apps. D-GSM (btw not limited to 2G) is indeed most interesting for routing "old style" voice calls and SMS. These are still in wide use, and arguably more stable than pure data links, which have to compete for bandwidth with other data (base stations can actively prioritise voice). If you think LTE (4G), then everything is already a data link at first sight; but most carriers still use CSFB, where the voice calls fall back to a 2G RAN.