I think it depends on the type of conversation, and who I'm holding one with. For calls, I don't get exhausted of talking with someone for a few hours but with texts I'm more quick to lose interest, or go do something else so conversations tend to be short and kept to a few minutes or up to an hour at most. And it also depends what we're talking about I guess! If we're chatting about common interests, watching a show together etc. it can go on for a while but if it's just like 'how are you doing' etc. then it's very very brief :p