Yeah, it sounds like telephone touch tones. Think of it as a paging system for aircraft. Thanks to this system, the pilots don't have to listen to hours of HF static as they cross the Atlantic. If a ground radio operator needs to contact a flight, they send out a pait of these tones that are specific to that plane to get the pilots attention.
CPDLC stands for Controller-Pilot Data Link Communications and is a data link between the aircraft and ground. It is used among other things to automatically send position reports.
If you already knew all of this, please disregard this post