Dialpad

Dialpad is one of the older VOIP to PSTN providers. Their website claims over 14 million users.

March 7, 2016: Switch.co has rebranded to Dialpad.

They provide PC-phone service using their Chameleon software. They support all kinds of NAT and some of strict firewalls also.

Recently they have added support for a Cisco ATA, SIPURA SPA-2000 and dpPhone using SIP protocol on a broadband connection. While this may continue briefly for existing customers, it is unlikely these will be supported by Yahoo.

They used to offer unlimited US long distance calls for $11.99 monthly charge, but they are no longer taking new signups – attempts to do so redirect one to signup for Yahoo Voice, which offers only prepaid per-minute options.
Currently their service is outbound only, website says inbound is coming soon.

In June of 2005 Yahoo officially acquired Dialpad.