Mobile Application for Microsoft Dynamics NAV

Hello everyone,

We are trying to develop new mobile solution for Microsoft Dynamics NAV .
And i want if someone can tell me which is the best way to achieve this, which methods can be used.
And should we need additional licenses(in Microsoft Dynamics NAV) for this solution.
FYI: This devices should be work online and also offline. Online a mean(make orders online, view inventory online, and post invoices), and offline(make invoices and save to app mobile-mobile database, and to have opportunity to send or get the data from/to NAVISION manually).

If you need further information, just don't hesitate to ask.

Thanks for your answers,

Best Regards,
bekio