I was wondering Erin, do you do calls using Skype? Or do you prefer using landlines only? I ask you this because it might be possible to record the reading if you do it on Skype. I haven't tried it myself yet, but here's a link:
How to Record Skype Conversations: Tools, Resources, Tips at Digital Inspiration
Two programs I found interesting were one called PowerGramo which is free as long as it's only 2 people, and another one called PrettyMay which is free but only records up to 30 minutes maximum (perfect for 20-30 minute readings ^^).
Skyping might save you some money on international calls as well.
Of course there's always the risk that someone's computer might crash during a reading, but I think it's worth the potential benefits.