I couldn't have run into that many Irish busy tones, as I never noticed before that they're slower than the British version.

The cadence appears to be 0.5 sec. on, 0.5 off, the same as standard U.S. busy signals.

British busy is 0.375 sec. on , 0.375 off, placing it halfway in speed between the American busy and reorder.

(Though both sound rather different to U.S. tones due to the single 400 or 425Hz tone.)