Yes its possible. 

You could build an application to do this and openvpms has a number of features coming in 1.8 to assist this sort of thing...such as appointment finders etc.  

The simpliest way would be to build a stripped back application based on the original openvpms installation, but with better web access perhaps using an oAuth token etc.

The security in openvpms is NOT strong enough to be webfacing in my opinion so you would need to build another interface.  HOWEVER you need to make sure the interface follows all the rules of the Openvpms business model.

Its one of those things thats on my todo list, but given the size of the job - keeps getting kicked to the bottom.

My be a good project

• SSO authentication for clients - google facebook etc - why rebuild the ark
• Link to client account via a Presupplied activation code via email or manually by practice
• Once linked
  • view Client details - update - review by practice
  • view patient detail  - and reminders
  • make appointments and confirm them
  • pay account balance and view balances.
  • No access to patient detailed patient history - or maybe configurable
  • No access to details invoice history - maybe configurable

Ben