For your first question I would say:
"I've got a call waiting."
For your second question, I wouldn't really phrase it that way, text message address just sounds awkward. I know I would never say anything like that.
I would be specific in which I was referring to (the person's email address or cell phone number").
So the probably best way to phrase it would either be:
"Could I get your e-mail address?"
"Could i get your cell phone number?"
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