I dont think it is her number on the back of the photo. The number Deckard dials on the Vid-Phon at Taffy's bar is 555-7583 which doesn't seem to be on the back of the photograph.
I was just rewatching blade runner and Bryant mentions that 3 nights ago the replicant tried to break into the Tyrell building so he sent Holden over to investigate the new workers. I suppose this me ...
I'd say that the business card would have been something that she would have had (if they used business cards still). I am certainly making one for my wallet. It would go a long way to explaining ho ...