A recent report from the UK's telecom watchdog Ofcom stated that VoIP usage by consumers is declining:

[quote]"A significant gap remains between the awareness of Voice over Internet Protocol (VoIP) and its actual use, with the number of users actually falling in 2008. This indicates that while
there remains a core group of consumers of VoIP services, the majority of broadband users
are still choosing not to use VoIP, perhaps because of issues over VoIP quality of service or
because of competition from low-priced fixed and mobile telecoms services."[/quote]

Of course the great irony here is that incumbent telcos themselves increasingly use VoIP technology within their networks, so we are all VoIP users in one way or another, and overall the number of VoIP users must have greatly increased. Ofcom no doubt are counting services like Vonage that piggyback VoIP over broadband into people's homes, or perhaps consumer focused services like Skype offering desk-to-desk VoIP.

There are other stories to tell, for example:

1. BT's 21CN project aims to replace the entire network core with SIP by 2011.
2. Wholesale VoIP is a growing business, selling bulk long distance and international calling to incumbent telcos and cellcos.
3. In many ways IP technology is already an integrated part of many telco networks, for example the widespread use of Sigtran to carry signalling traffic over IP, perhaps also using non-TDM bearers with protocols like BICC.
4. The GSMA are promoting a protocol called IPX that will allow cellcos to connect to each other using IP, eliminating legacy TDM interconnects. Your mobile to mobile calls could in the future be IP only.

Increasingly the distinction between 'old networks' and VoIP are blurred because telcos know how to use IP too. I don't expect to ever see 90% of UK households using VoIP phones over their broadband connection, but for sure 90% will soon be using IP in some form, if that is not already true.