While it would be convenient to just have a single control that operated all three Tstats and heat pumps at once, it would eliminate the advantage you gain by having multiple heat pumps. Zoned systems allow for different temperatures in different areas, and at different times. They also allow for more specific response to different conditions such as a warmer 2nd story that needs to be cooled more than, say, a basement area.
So you might, as suggested, gain that convenience via an automation system (Elk, ISY, HAI, etc.) which could control all three at once through "scene" type programming (one interface controls each Tstat simultaneously), but also find yourself wanting to control each Tstat separately in man situations.
The Nest was mentioned, and I find it works very well, with little need for us to interact with it to adjust it. For your situation you could just have 3 little icons on your phone, all lined up, for when you want control. But each Nest itself would handle the bulk of your actual control without a need to touch them (they'll even program themselves to a large degree as they learn your schedule, if you wish).