The OBi has no control over what other people have to dial on their telephones to reach your number. If you actually meant you can't dial out using 7 digits to make local calls, make this change:
Voice Services -> ITSP Profile A -> General -> DigitMap:
(1xxxxxxxxxx|<1>[2-9]xxxxxxxxx|<1aaa>[2-9]xxxxxx|011xx.|(Mipd)|[^*#]@@.'@'@@.)
where aaa is your local area code.