I finally was able to contact my dentist. They use a weird system where there is only one way to contact them; A phone line that ring 4 time, available 10h-12h, and if no one answer it just hang up automatically. No mail or other way to contact them. And no one ever answer.
So I set up an Asterisk-FreePBX server with my number at voip ms and made the system ring them none stop and connect me via my cellphone upon success
Took them ~1.5 hours to respond... The women was pissed ^^' (372 calls)