Call when you want
But there's no one home
And you're not going to reach my telephone!
Out in the club
And I'm sipping that bub
And you're not going to reach my telephone!

from Lady Gaga (Ft. Beyoncé) – Telephone Lyrics on Rap Genius

Meaning

She’s basically saying that it’s senseless to call her because she’s in the club, not at home and thus can’t reach her telephone.

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