In the United States, the FAA's Aeronautical Information Manual, section 4–2 "Radio Communications Phraseology and Techniques," states the following (emphasis in original):
4–2–3 a Initial Contact.
The terms initial contact or initial callup means the first radio call you make to a given facility or the first call to a different controller or FSS specialist within a facility. Use the following format:
- Name of the facility being called;
- Your full aircraft identification as filed in the flight plan or as discussed in paragraph 4-2-4, Aircraft Call Signs;
- When operating on an airport surface, state your position.
- The type of message to follow or your request if it is short; and
- The word “Over” if required.
So on initial callup you should state the facility being called followed immediately by your callsign.
Then later in the section (emphasis mine):
4–2–3 c Subsequent Contacts and Responses to Callup from a Ground Facility.
Use the same format as used for the initial contact [...] The ground station name and the word “Over” may be omitted [...] Acknowledge with your aircraft identification, either at the beginning or at the end of your transmission, and one of the words “Wilco,” “Roger,” “Affirmative,” “Negative,” or other appropriate remarks [...]
Thus the proper procedure is:
- Use your callsign at the beginning of any subsequent transmission (e.g. a request or report), but
- When acknowledging an instruction (such as a takeoff clearance) you may use your callsign before or after the acknowledgement.