are they using a proprietary system?

my sister works for this marketing company and they first let their PABX get so old it was desupported, and then rushed in a new Avaya [1] system which took about 3 weeks to be usable (a long time for a marketing company with a call centre!)

the “project manglers” managed to knock out the entire E1 circuit (30 lines – ouch!) and didn’t set the echo cancellers at first :you_crazy

[1] I always read that as “aiyaa”, which is what Malaysian Chinese often say when stuff malfunctions or goes wrong! (but despite movie stereotypes not when doing karate/judo, this is done silently with the odd grunt or two)

I am probably working on a far smaller system (3 sites maybe 50-100 endpoints, 10-25 trunks max) but feel free to send me a PM if you want any advice.

the main problem with VOIP implementations is trying to save a few cents in the sort term, lack of contingency plans in the early stages and the fact that many IT/networks people do not understand some aspects of conventional telephony (which you need to know when connecting to the normal telecom circuits)