Paired with 얼마나 or 어찌나 in front, it exclaims about a past experience: how precious and sweet it felt, how excited he was that you were coming, how good the community bikes are. Its other use in these lines is the offhand 'or you could just...' — call within a month or whatever, change the name of the content or whatever, break your nose while you're at it. Careful with the spelling: standard Korean writes 든지 for the 'whichever' sense and keeps 던지 for looking back at the past, but speech does not distinguish them.