Adhan announces the prayer time to people who may not yet be present, so measured articulation is appropriate.
Iqamah signals to an assembled congregation that prayer is about to begin, so it is delivered more continuously.
This is a distinction in purpose and manner, not a distinction in whether the prayer itself is obligatory.
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Bab al-Adhan: The Adhan, Iqamah and Juristic Rulings
Adhan announces the prayer time to people who may not yet be present, so measured articulation is appropriate.
Iqamah signals to an assembled congregation that prayer is about to begin, so it is delivered more continuously.
This is a distinction in purpose and manner, not a distinction in whether the prayer itself is obligatory.