Ebay (EBAY) rolled out Skype’s unlimited calling plan in a bid to keep up with rivals and – let’s face it – to finally land some paying customers.

For $2.95 a month. U.S. Skype customers can make unlimited calls anywhere in the United States. Calling plans from the United States to Europe cost $9.95 a month.

The move comes amid speculation that eBay might be considering a carve-out option for the voice-over-Internet-protocol, or VOIP, service that counts 309 million registered users.

eBay’s $4 billion Skype bet hasn’t paid off as the company hoped when the deal was signed in 2005. Last year, the online auction shop took a $1.4 billion charge to write down some of the unrealized value of that deal. This year, some eBay investors are hoping for a different sort of transaction – a sale.

“This is something that belongs with another entity,” says Darren Chervitz with the Jacob Internet Fund, an eBay investor. “Skype makes more sense at a place like Google (GOOG).”

Skype software allows PC users with microphones and cameras to make free calls to other Skype users or cheap calls to conventional phones. The service was expected to enhance communication between buyers and sellers in eBay’s auction market.

Big tech companies that generate a lot of cash are justifiably wise to make bold bets on innovative acquisitions, says Chervitz. Sometimes it works, like eBay’s purchase of PayPal, and other times it doesn’t, like with Skype, he says.

Chervitz would like to see eBay get some value back from Skype while it still can. “They should sell it now, says Chervitz, “before the technology changes.”