We had one once, years ago at a Bank with a 120 line PBX, 20 CO Trunks. Customer calls in Monday morning from the pay phone - furious! Every call they make outgoing gets a wrong number. Internal calls work fine. Test the trunks from the demarc - they're fine. You can dial with a butt set and get through every time.

Must be the PBX - but how?

Turns out the customer wanted tone dialing and the CO (at that time) only offered rotary. So we gave the customer tone to pule conversion. All was well for the first year.

Over the weekend telco converted the exchange and programmed the customer (probably defaulted the whole exchange) for mixed tone/pulse dialing. The customer had all tone dial sets. Dial "9", get an outside line. Start dialing 555-1234. By the time you've got the 555 out the outpulsers have repeated the 555 so now you've dialed 555-5551. Or something similar.

Drove us nuts till we figured it out. The Bank wanted to sue for lost revenue. Telco refused to see it as their problem.

But they did come back later and bill the Bank the extra tariff for tone dialing trunks.

Sam

"Where are we going and why are we in this hand basket?"