Assertion: whistle's frequency | /r/HasProperty | mf
Facets:
Source sentences:
text: The end of multi-frequency (MF) phreaking in the lower 48 United States occurred on June 15, 2006, when the last exchange in the contiguous United States to use a "phreakable" MF-signalled trunk replaced the aging (yet still well kept) N2 carrier with a T1 carrier.[citation needed]