With the ModemManager 1.25.95_git20260422 upgrade in aports, DTMF tones no longer work reliably on the PinePhone. This means that if you're calling an automated system, pushing the keypad buttons may not have any effect. It has not yet been confirmed at the time of writing, but the PinePhone Pro is likely affected as well given that it uses the same modem hardware.
While no root cause has been identified, downgrading to ModemManager 1.24.2 works around the problem. Help with further diagnosis and bisecting is very welcome! See the relevant issues for more information.
Note that downgrading to ModemManager 1.24.2 has the side-effect of breaking the cell broadcast feature.