Lars,
In general Advantage is licensed per concurrent user for all LAN users. If you are accessing Advantage data through a middle tier, such as a web server, you need to purchase an Advantage Internet Connector (AIC) license.
With the release of version 11 we also added an option for mobile devices called the Advantage Web Platform which is licensed per device.
Based on your question I would recommend purchasing an AIC license and at least 10 additional user licenses to cover your LAN users.
You should contact your sales representative or send an e-mail to AdvantageInfo@SAP.com for pricing information.
Chris