Reorder tone

In EU countries and those following ETSI (European Telecommunication Standards Institute) recommendations, the cadence is the same as North America, i.e. 0.25 seconds on / 0.25 seconds off, but with a 425 Hz tone.

[1] A PBX also often indicates an invalid extension, while dialing an invalid telephone number on the PSTN usually results in playing the triple special information tone and a recorded announcement.

Some European networks may return the reorder tone as a generic error signal for invalid or incorrect numbers or where a particular call type is not supported or has been barred.

Some switches, notably in Europe where open dial plans are used, analyse a number as it's dialled, and may even return a reorder tone before the complete number is dialled if the initial sequence of digits are invalid.

The reorder tone is sometimes confused with the busy signal because they use the same frequencies and differ only in that the busy signal's beeping sounds have a slower cadence than those of the reorder tone.