The so-called AIM Phoneline service would be the first to come with a free number that could receive incoming calls from any type of phone. One of the most popular VoIP services Skype charges users about $4 per month for a phone number.

AOL’s forthcoming focus on VoIP, which may launch in May, is a consumer play for sure. But businesses should keep watch because consumer VoIP services have historically made their way onto worker’s desktops and often are a launching pad for more enterprise-class services from vendors.

AOL also plans to launch an upgraded version of its service, AOL Phoneline Unlimited, which will let users make outgoing calls for a flat $14.95 a month fee. Users will be able to make unlimited calls to all local and long-distance numbers, as well as about 30 overseas countries.

Phoneline will work much the same as existing VoIP services, except users must be logged onto AIM.

AIM currently has some talk features, but Phoneline promises to be more robust and will be integrated with AOL email so that users can click to talk and hear voicemail, also a free service.

Apparently, callers to Phoneline will be graded by their reputation. A telemarketer, for instance, would get a low reputation score, which would show up when they called so that users could choose not to answer. Phoneline also may ping a user’s mobile phone if a call to their computer goes unanswered.

While there were 47.6 million AIM users in March, membership had dropped 13% from a year ago, according to Nielsen/NetRatings.

But Dulles, Virginia-based AOL hopes to turn that tide and is planning to launch AIM Pages, which would compete with MySpace, an interactive community of personal web pages.

And AIM is AOL’s most popular product. AIM dominates the online chat market with a greater than 50% market share.

Phoneline may well put the pressure on Google Inc to add inbound and outgoing call capability to Google Talk. Currently, Google’s IM VoIP service is only PC-to-PC.

Google will hold a rare Press Day at its Mountain View, California headquarters on May 10, and there is speculation the search company will use this opportunity to announce a beefed-up VoIP service of its own.

Just when Google is likely to launch a more complete VoIP offering is unclear, but it does seem likely. After all, Google’s main rivals, Yahoo and Microsoft, are steadily improving their VoIP services.