Interesting to see that Belgacom ICS , the fourth largest wholesale voice provider in the world, has completely changed over to a VoIP core using Sonus Networks kit. The project, which migrated the equivalent of more than 10,000 E1 TDM and SIP trunks, took only 15 months.
There will be massive cost savings for Belgacom here. Often the business case for this type of migration is justifiable on purely the savings in electricity used to run the old and inefficient TDM switch gear.
In the UK we have the BT 21Century Network but I am not aware that BT has yet undertaken an activity on the same scale as Belgacom. Certainly it has put off migration of exchanges until 2020.
Coincidentally I recently had Sonus in for a chat to look at their new Session Border Controller. Check out the post here.