Normally, the OBi interprets and acts upon *xx Star Codes. If you'd prefer the OBi ignore them and instead pass them on to your service provider, you will need to set:
Physical Interfaces -> PHONE Port -> StarCodeProfile : None
and add a rule to the ITSPA DigitMap to allow them:
for 2-digit Star Codes : *xx|
for 2- or 3-digit Star Codes : *xxx?|