Student Pilots: Say These Exact Class D Calls (14 CFR 91.129, AIM 3.2.5)
You must establish and maintain two-way radio communications with the ATC facility serving the Class D area before you enter, and you must keep that contact going the entire time you are inside. A controller reply that uses your callsign, even a simple "standby," means you are cleared to proceed toward entry. Anything less, and you stay clear of the boundary until you hear your tail number.