"When departing from a towered field (Class C or D) on an IFR flight plan, do you wait for the tower to tell you to contact departure frequency or do it after you are airborne without instruction from the tower?" - Andrew
“Always wait for the tower to issue instructions to contact departure. The controller may be keeping you on the tower frequency to resolve a conflict in the local traffic area.
If you have flown a reasonable distance – a mile or two – and still not have been transferred to departure, ask the tower. The controller’s first transmission may have been blocked or just simply forgotten.”