The survivors at the quarry hear Rick on the radio in episode 1x01 "Days Gone Bye". Lori and Shane have sex in the woods and Dale picks up another radio call in episode 1x02 "Guts". Rick arrives with the new group of survivors and reunites with his family in episode 1x03 "Tell It to the Frogs". Appears in 2 more episodes.
Source: The Walking Dead Map