Former shareholders of Tourmaline Networks have filed a lawsuit against Nokia and its subsidiary Intellisync, claiming the top handset maker “willfully” violated its merger agreement.

In March 2005, Intellisync acquired Tourmaline for $4.1 million; in November, Nokia announced its $430 million acquisition of Intellisync. Part of Tourmaline’s merger agreement included earn-out provisions based on revenues earned from Tourmaline products the following year.

In a statement, Troumaline shareholder’s law firm said: “The lawsuit alleges that Intellisync and Nokia failed to make reasonable and good faith efforts to promote and develop Tourmaline products and actively impeded efforts to meet the minimum earn-out provisions provided by the merger agreement.”

The suit claims that Intellisync was creating competing mobile e-mail products and directing resources away from development and promotion of Tourmaline products. Shareholder lawyers claim that Troumaline was one of the first companies to create software that allowed consumers to access e-mail on their cell phones.

The case is expected to go to trial May 9 in North San Diego County Superior Court.