I have a DK424 with a RPTU or BPTU (cant remember which) and today I get a call telling me: when I press 9 to get an outside line I get the dial tone and dial a couple digits of the phone number and it goes to a busy signal. When you try to call in all I get is blank air. I had them power cycle the Dk and the phones all now work fine, inbound and out. I dont have a spare BPTU so I cant swap that out with the hopes it doesnt do it again. Anybody have this problem before?

The PRI may have lost sync with the central office. The DK424 were not too good at recovering from sync errors.