English to Russian Tech/Engineering Computers: Systems, Networks

Certainly - at least in the short, or even the intermediate terms - the core business of an Avaya or Nortel isn't threatened by IP PBX hosting. There'll likely always be a vibrant market for premise-based telecom solutions - Centrex, after all, didn't kill the PBX business. And even if hosted PBX starts looking like a profoundly more cost-effective strategy for business, it'll take years to uncouple, recode, and reintegrate all the apps now binding CPE to the enterprise.
Unless, that is, PBX makers recognize the branding and market opportunity inherent in every phase of the market's migration to hosted IP solutions, and choose to embrace hosting, rather than agitate against it, or refuse to play.