KMobileTools is an OpenSource project (GPL2 license) that aims to be a complete management system for mobile phones.
It's written in C++ using Qt and KDE libraries. It's using KParts technology, so it can be embedd in every application (like in Kontact), it can read and write KDE AddressBook, full import/export, read and write SMS, export them in KMail, and much more. All this depending on your phone capabilities, of course. Developers

• Marco Gulino ("RockMan", marco AT kmobiletools.org) Public GPG Key.
  homepage, english blog, italian blog
  Project management, libraries development, AT engine, webmaster.
• Matthias Lechner ("matlec", matthias AT kmobiletools.org)
  Gammu engine, main API redesign.
• Stefan Bogner ("Bochi", bochi AT kmobiletools.org)
  Gammu engine, various stuff.
• Sérgio Gomes ("sgomes")
  Siemens fixes to AT engine