Well, just answer the PHONE.
The Big Bang Theory Season 3, Episode 14
(PHONE RINGING)
The Big Bang Theory Season 2, Episode 22
(CELL PHONE BEEPS)
The Big Bang Theory Season 4, Episode 1
(PHONE BEEPS)
The Big Bang Theory Season 6, Episode 2
(PHONE BEEPS)
The Big Bang Theory Season 6, Episode 8