(^O^)／

What is the meaning of 일때면?

during.

What is the meaning of 메세질

message

남겨놔 is 남기다 ....?

남겨놔 means past, 남기다 means present.

대체 means 一体？

대체 means why???

What is the meaning of 일때면?

when

어쩌다 like how?

sometime
어쩌다 can be "how" but in this sentence it means how. So 어쩌다 통화중일 때면 means
when you're phone is busy sometimes

What is the meaning of 메세질

make short "메세지를" 메세지+ㄹ and omit ㅡㄹ
you know 메세지 means message

남겨놔 is 남기다 ....?

남겨놔 means leave your message in here. literally make someone to leave something
남기다 means leave

대체 means 一体？

대체 is 도대체's short form. means well... like what the!!
we use it to emphasis something