I have a similar issue with my BV6000s and I believe I can offer some explanation as to why you cannot designate specific phone numbers to a specific SIM. The BV6000s does not activate both SIMs at the same time. By that I mean when you select a SIM as your "Preferred SIM for Cellular data"...

I have recently purchased a BV6000s and find that I cannot use both SIM accounts at the same time. Only the SIM designated as "Preferred SIM for Cellular data" is functional. The other SIM, while recognized, will not send or receive calls or SMS messages. Is this a design flaw of the BV600...