phone tones and Keith Doxey's help?

[Adrian <yahoo1@xxxxxxxxxxxxxx>]

Hi

thought Keith would be the man for this but maybe someone else has the
knowledge.

short story, after upgrading from comfort 1 alarm system to comfort 2
(yes, you may have seen this on the comfort tech site but are after more
tech detail to help solve this issue), when people leave a message on
comfort 2's answerphone, it doesnt detect they have hang up and records
a continuous tone (comfort 1 never had a problem with this)

so whats this tone called (sounds like dialtone but higher pitched) and
what frequency is it at? any weblinks that might explain this?

thanks in advance

Adrian