Free phone number

Hello all,

I got to know this friend (B) of my friend (A) who I met when I hangout with my bro (Z).
Just got to know that A is single but I'm not interested in her but her friend, B who's also single whom I haven't met.
Due to some turn of events, I got B's phone number but not A whom I used to meet before and never asked for her number because of I'm not interested.
How do you suggest I introduced myself to B whom doesn't even know me & I also don't even know her? call or whatsapp or message or any other method?

why would you even contact this person????

I happened to 'see' B through my friend's fb pic & found her cute, that's what started it