With the $20 Monthly, $30 Monthly and Pay Your Way:
It's $0.20 per minute (plus airtime) to call from Canada to the US. For $10 per month you can have unlimited calling to the US. It's also $0.20 per minute to call from the US back to Canada.
With the $40 Monthly and $33 Monthly:
It's $0.05 per minute (plus airtime) to call from Canada to the US. For $10 per month you can have unlimited calling to the US. It's also $0.20 per minute to call from the US back to Canada.