It is all well and good that SIP trunk providers like Voiceflex are boasting that they are using secure data centres for their switching. But their customers lost service for an hour and 20 minutes on the 6th July 2011. They had 2 other outages in the last 12 months that I know of. This means nobody can make or receive calls and it’s very debilitating.

Apparently there was a power outage at Telecity Harbour Exchange 6/7 (HEX 6/7) in London Docklands and the backup power failed to initiate. Is the world really ready for this sort of telephony?

That's why i'd never supply a system with ONLY sip trunks on it. Simple as that.

The technology exists to run SIP based trunking but i'm not convinved the network is quite there yet - not just from the ITSP / DR point of view but also from the point of bandwidth and contention.

Personally I deploy SIP trunks as a back up to the traditional PSTN / ISDN Trunks and use the SIP as a failover route if the ISDN fails. I also use SIP to allow out of area numbers to be presents to / from the PBX