While I agree that sending the email would have been a poor choice, I have the same initial reaction to the "training call" as the OP - and even more so once learning that the call was going to take an hour.
If an MSC wants every shopper on a project to go through an unpaid hour-long training call, that is absolutely and positively their prerogative. However, it is a matter of respect to include such expectations in the initial job description, known before the shopper takes the shop. $25 is barely enough to get many shoppers to even make a visit. It's not enough for others. Adding an hour-long phone call would take the shop well out of many of our "Is it worth it?" qualifications. I would also be perturbed if I were to be on a required training call specific to a shop and find that it was more of a introduction to mystery shopping course. Such calls should be concise and focused on the project.
I recognize that there is a huge turnover of shoppers and that shoppers from all sorts of backgrounds and with all sorts of skill sets sign up for every MSC and that MSC's can struggle to find folks willing (and able!) to complete their visits - so they find it necessary to try and train their IC's to do a job well. However, as a matter of respect and principle, they should be up front with this - not springing it on experienced shoppers after they have accepted an assignment.
Create the online training modules. Have us pass certification tests. If you have a really special project that needs more personal attention, sure, have a training call - but make the expectation known ahead of time.
Hard work builds character and homework is good for your soul.