Form 55 takes the digits as received by the system and allows them to be modified before presenting them to the PBX.
It is optional whether this is done or not.
It has no effect if no translation takes place
It is completely independant of the NSU programming
NSU receives call, NSU passes digits on to PBX, PBX modifies Digits (or not) and presents digits to Dialed Number.
The (or not) above refers to FORM 15 Modification AND/OR for 55.
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What's most important is that you realise ... There is no spoon.