"Can I call you sometime" is a terrible line to use to get a phone number. Girls will often play a game here and give you mixed messages.
Be manly and just suggest that they give you their number.
"No" is not a mixed message.
And sorry, I'm not going to "act manly" to impress a girl. The guys who "act manly" are generally the guys who treat their girls like crap and make girls whine about never being able to find a nice guy. That's not my schtick, sorry. I am who I am, and if a girl decides I'm not worth it because I said "hey, can I call you tomorrow" instead of "give me your number, bitch" then she certainly isn't worth it either.