Videoconferencing firm Tandberg was all too happy to accept Cisco's $3 billion buyout offer back at the beginning of October, but at least two investment consulting companies say Cisco's bid undervalues the firm.

The only opinions that matter at this point are those of the Tandberg's shareholders, who have yet to approve the deal. Before the agreement can go through, owners of 90 percent of the company's shares have to give it the green light, and do so by the end of the day today. There's been talk that holders of 24 percent of Tandberg stock don't plan on signing off on the deal, and should that happen, Cisco has hinted it would walk away rather than raise its offer.

"We believe we are paying a fair price for a quality asset, and our offer comes recommended by the Tandberg Board of Directors," Cisco said in a prepared statement. "Further, Cisco's general approach to M&A activities is that no acquisition should be pursued or completed if it runs counter to the broader principles of prudence and financial fairness."

But not everyone agrees with Cisco's assessment. Consultants from Panta Capital and Scott & Associates contend that Tandberg's third quarter financial results beat the consensus estimates of analysts for revenue and profit, and Cisco's offer simply isn't enough.