If you can keep a stimulating conversation going for hours at a time, by all means, but don't make it a habit.
Tailor your phone time to your own conversational capabilities. If you aren't too much of a smooth talker on the phone, then don't bother having any long and intellectual phone conversations. If you can keep a strong verbal front, push your advantage and have some good conversations.
On average, your phone conversations should not exceed 45 minutes each. I usually like to set a lower standard, so it will be easier for me to progress and show connection as a slowly increase call times. Test your own capabilities then figure out your own "perfect timing" for calls. Report back and give us what you find.
-Damian
