[asterisk-users] BT line: unavailable vs withheld numbers?

[A J Stiles]

On a BT line, how do I determine whether the number on an incoming call has 
been deliberately withheld  (by dialling 141)  or is merely unavailable  (e.g. 
because it originated from overseas or passed through some ancient switching 
equipment)  ?

In the first case, I want the caller to be played a message to the effect that 
we are not at home to anonymous cowards but if their business is important, 
they may redial without withholding their number.  In the second case, the 
call needs to be treated as legitimate since it is not really the caller's 
fault that their number is not available.

Software is Asterisk 1.8.5.0 with DAHDI 2.4.1.2.  Hardware is TDM410P with two 
each FXO and FXS modules.

-- 
AJS

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