The client interfaces that we have seen earlier require the user to be connected to the Internet, and they don't work in an offline mode.
There are some considerations to keep in mind if our environment uses CRM on premise, and we want to let our user access the CRM data externally using the mobile devices.
Most of the mobile clients will be located outside the local network; so if we are working with an on-premise environment, we will have to enable Internet-Facing Deployment (IFD). This means we need to change the authentication method from an integrated windows authentication to a claims-based authentication that requires the deployment of the Active Directory Federation Service (ADFS).
Enabling a claims-based authentication will also force us to implement the HTTPS protocol that will also require us to purchase an SSL certificate. A 2048-bits SSL certificate is recommended. It can be obtained on Verigin.com or Godaddy.com...