If you did any defaulting, the commission system message may be present on ext20 inplace of the date/time?

If it is, you need to commision the system (basically logging the system with the BTs old RACE system).  You use the commission menu to do that - you enter the main phone number as the ID etc.  The system then grabs a line and connects to BT, the commission message then vanishes.  This is simply done so BT know when a system has been installed and finished when installed by them, but running the commissioning routine as a private installer has no backlash at all.  You can remove the commission message by editing the XML file too, but easier to let it run through!  If you don't have the mesage on ext20, you have no prob anyway!  Even with the message everything will continue to work.  The menu option will have always been there (I am pretty sure).

Glad you have it sorted and have sorted out the numbering.  Rare to find that the system will respond in both P-P and P-MP, you will usually find it will function with only the correct one.....