Plaxo, the online address book company, has announced plans to acquire HipCal.

HipCal develops an online calendar, to-do list, and address book. Plaxo, which would not reveal what it paid for the company, plans to integrate HipCal's technology into its free service, company officials say. Plaxo will also develop premium calendaring services based on HipCal, therefore creating a new revenue model for the company.

"We plan to do for the calendar what we did for the address book," says Ben Golub, president and CEO of Plaxo, in a prepared statement.

HipCal's five founders, who were fraternity brothers at Rensselaer Polytechnic Institute, will become Plaxo employees. Plaxo will keep the HipCal service up and running during the transition, officials say. Plaxo's self-updating address book is accessible from any web-enabled device, giving users access to their contacts from wherever they may be, officials say.