WebIS Mobile Sync is by itself just a client to the Plaxo service. The Plaxo service is a central repository for your PIM data online. Install the desktop client for Outlook, Thunderbird, e2xo for Macintosh, or other forthcoming plugins to sync your contacts any time you have an internet connection on your device. Even if you currently only use Outlook and ActiveSync - consider the ability to sync certain categories with a home desktop and certain categories with a work desktop! Consider the superior synching matching abilities of the Plaxo service compared to ActiveSync. Consider having your contacts always updated directly from other Plaxo members!
Why not just use ActiveSync?
Great question! ActiveSync, even it its fourth rendition, has some serious issues with its synchronization logic. Duplicate and general conflict resolution does not always work and duplicate PIM entries can be a problem for some. Furthermore, it only allows synching with USB or Bluetooth connections. Mobile Sync works just like the Plaxo Client Outlook plug-in (except it runs as a stand-alone application): register your Plaxo account and hit the Sync Now button. Super simple.