phoning south dakota blocked

I phoned a number with a South Dakota area code. On my personal phone, it's no problem. Using RingCentral, the number is blocked and needs to be enabled by an administrator (i.e., me). Since I can block only incoming calls, this made no sense. RingCentral support told me that North and South Dakota calls are blacklisted by default, and I'd need to fill in a whitelist request. It does not seem possible that RingCentral has blacklisted domestic area codes. Has anybody else experienced this? And is there a sensible explanation?