I've been involved in call center training, not for work-at-home reps but the basics can still apply with a little creativity. There are a few components to consider - you obviously want to start with "what knowledge and skills you need to train them on". For example, if you start new hire orientation topics such as company policies and procedures, job role expectations, etc. you can easily do webinars or create online courses that track progress/completion that you can re-use. For webinars, I would just recommend for everyone to have a mic at the least and a webcam if possible, at least for the trainer. When you get into more role specific topics, such as customer service, conflict resolution, handling difficult/irrate customers, communication skills and such, you could easily do it over webinars as well as long as you treat the environment as a "virtual clasroom" and not just a call/online meeting. Make it interactive, create activities and even pre-session assignments. You can record your reps and then get together and evaluate and provide feedback as part of the training. You can have mock calls with different type of customers and train that way.
I hope this helps - if you plan this out carefully, put some good structure around it, specific guidelines and well defined metrics, it should work just fine.
