The mobile device syncs to the ACT! Connect Portal, but entries from ACT! Pro 2012 do not make it into the portal, and nothing from the portal makes it into ACT!.
It seemed to stop working around about the time of switchover to British Summer Time (clocks moved forward 1 hr in the UK).
To remedy (after much messing about!), I first stopped the ACT Connect service (from right-click of the sync app in system tray), and then exited the sync/connect app from the same right click menu, and went into c:\documents and settings\all users \application data\act\mobility, and moved all the files there into a directory called old (basically I deleted them, but backed up just in case).
Upon restarting the ACT! Connect program, a new sync began, and everything has made it into the portal. We’re about to test portal -> program sync, but I’m sure it’ll be OK.
On Vista/7/8, the directory would probably be C:\ProgramData\Act\mobility – basically it’s the “All Users” profile appdata.
I should add that I did a “recover” from the sync applications right-click menu first. This clears out everything in the portal. It might not have been necessary, or maybe you’ll get duplicate data if you don’t do it?