Thinking about Phil Simpson's comment, "context of the users"... I see a big difference between business-process and mobile-applications. The context, from my experience, is a person working at their desk and/or home office. The phone (mobile device) is then an extension of the work-environment. This is the context.
Now I'm not saying that the phone doesn't have a place within BPM systems - they do. But, that place is very limited outside the formal work environment (where work gets done) - meaning that I'm not so sure a phone fits too well as a BPM system device (user-interface) outside commonly understood telephony (telecom systems). So, what good is a smart phone outside the context of say... CRM? Where's the process fit behind our common BPM drivers:
High-value workers usually get more work done within the office context. Outside the office a participant's business value is reduced to a recovery effort of lost time. The worker is significantly disadvantaged given the limited process-toolset available within your common smart-phone.
Basically, the smart-phone is stuck as a point-solution (phone app' host) for the time-being. Something like 'google-glass' can change this perspective... but not yet.