I have a specific scenario in mind, but I will ask this generally:
Is there a way to make my mobile phone trigger an action on my computer? I am thinkin
'depends'
you'd need to check the SDK for the phones you're targetting - but Symbian and certainly WindowsCE phones can do that (NFI about the iPhone).
Calling into Dynamics would be easy from a webservice, you could expose that either internally or externally and thus use either WiFi in the area (be it your own corporate network, or a hotspot) or data over the mobile phone network.
From days working in Microsoft CRM (hellish days of v 1.*) there were mods to do what you talk about using either Skype or regular landline phones then, I'm sure writing stuff for it has improved since when it was craptacular.