Hot on the heels of Yahoo!’s announcement of penny-per-minute VoIP to PSTN calling from their IM client, Microsoft and SIPphone are both jumping into the ring. Microsoft has announced a partnership with MCI to provide PC to phone calling in the near future, though at a disappointing 2.3 cents per minute. But SIPphone stepped right up to the plate offering standard 1 cent VoIP to phone calling rates anywhere in the U.S. Key industry watchers like Om Malik and Andy Abramson are declaring that the price war is now officially on.

This field is going to get crowded quickly, and it will be interesting to see what impact all the competition will have on the costs of getting from VoIP to the PSTN. Not to mention how Skype will fare now that the big boys have started moving into its territory. As services ratchet up and new applications emerge will we see free calling between the public telephone and the IP networks?