The announcement, according to an article in Sunday's New York Times, will immediately make available a free software download for the Apple devices. The software for various BlackBerry models will become available in May. The announcement is expected to be made at a press conference just before the opening of the CTIA wireless conference in Las Vegas.

Voice Only on Wi-Fi

The announcement by Skype, a division of eBay, is attracting attention because of the possibility that it might signal yet another step toward free or nearly free voice service on mobile devices. Originally launched as a free computer-to-computer voice and then video communication, Skype on mobile devices will allow users to make voice calls and send instant messages to other Skype users over Wi-Fi connections.

Skype users can also call the landline or mobile phones of non-Skype users for a small fee that is less expensive than normal cellular rates.

In the incarnation being released this week, Skype won't work on the high-speed data networks from the wireless carriers, like AT&T's for the iPhone. However, users will reportedly be able to text chat with other Skype users via AT&T's EDGE and 3G networks.

According to news reports, Skype for the iPhone has the look and feel of that device's interface, and users will be able to mute callers, put them on hold, or have the call on speakerphone. Features such as conference calls or taking a second call will not be available in this first release.

Skype has already announced versions for devices running the open-source Android operating system from Google or Windows Mobile from Microsoft, and for Nokia phones.

Not 'Much of a Threat'

Industry observers will be watching the new Skype versions closely. Not only do they raise the possibility of Voice over Internet Protocol (VoIP) service that could undercut the carriers' plans, the announcement also makes a phone-less device like the iPod touch into a kind of phone.

But Bill Ho, an analyst with industry research firm Current Analysis, said Skype is "not that much of a threat right now" to the carriers. He noted that, in its free mode, the user needs to be in a Wi-Fi hot spot, and the phone conversation partner also needs to be on Skype and in a hot spot.

Skype on these mobile devices could be "pretty powerful" in terms of convenience when traveling outside the U.S., he said, but inside the country the advantages are modest "unless one has a lot of Skype friends." He noted that the new versions will still have a "wow" factor, but the need to plan your calls lowers the convenience factor.

Ho added that the Skype-ization of the iPod touch, however, "is very interesting," since that device now becomes a kind of limited iPhone.