for critical telephony applications.. Avaya jud ang maayo.. infact naay thread sa linkedin.com comparing avaya vs. cisco and others.
I've been an avaya engineer since 2004... user pud ko ug asterisk..
altho my avaya runs on a cisco network.. and preha with most others..
either avaya or asterisk.. naa gihapoy downtime.. sa avaya mostly trunk downtime (telco related and/or network related issues, usahay hardware issue).
akong asterisk hosted (vps) sa US and naa dapoy downtime altho minimal lang.
comparing avaya to asterisk is like comparing apple to orange so dili jud match.
if naay budget ang company nya critical ang requirement avaya nalang.. infact naay namaligya karon ug refurbished avaya (G3R lang noon) and been using it to extend my corporate locals to 2000.. am using S85xx for the call center w/ CMS & Verint voice recording.
if anyone need a refurbished avaya i can help you but it's not recommended for call centers.. pang office locals lang noon w/ a ACD..
Asterisk is just used for my integration experiment.. if anyone also need a cheaper linux VPs ($2.95 a month), i can also help
i wish there's a pinoy group for all things telephony (avaya or asterisk) helping each other sa mga configuration, issues, troubleshooting, etc and job hiring... been a member of some groups but mostly dili mga pinoy ang naa.