Preventing iPhone from Syncing Automatically

You may want to prevent iPhone from syncing automatically if you prefer to add items
to iPhone manually or when you connect iPhone to some other computer than the
main computer you sync iPhone with.
Set iTunes not to sync automatically when you connect iPhone
Connect iPhone to your computer and in iTunes click the Summary tab. Then deselect
“Automatically sync when this iPhone is connected.” This also prevents iTunes from
opening automatically when you connect iPhone. You can still start a sync manually.
Set iTunes to prevent automatic syncing for all iPhones
In iTunes choose iTunes > Preferences (on a Mac) or Edit > Preferences (on a PC),
then deselect “Disable automatic syncing for all iPhones.”
If this checkbox is selected, iPhone won’t sync automatically, even if “Automatically
sync” is selected in the Summary pane.
Prevent iPhone from syncing automatically one time, without changing
any settings
Open iTunes. Then as you connect iPhone to your computer, press and hold Command-
Option (if you’re using a Mac) or Shift-Control (if you’re using a PC) until you see iPhone
in the iTunes Source pane.
Start a sync manually
Click the Summary tab, then click Sync in the lower-right corner of the window.
Or, if you’ve changed any sync settings, click Apply.