Okay, so for anybody who is curious. My old ToS which does not specify that they can add any charges they like is no longer void. In it (and in their current ToS) they have this:
If you do not accept a change to these Terms, your sole remedy is to retain the existing Terms unchanged for the duration of the Commitment Period (as efined below), upon notice to us within 30 days of your receipt of our notice of change in the Terms.
So, they can mail you out a new ToS, and unless you called within 30 days of receiving it you are now bound to the new ToS. And, in the new ToS they have the following:
Unless otherwise specified in the Service Agreement, we may change, at any time, any charges, features, content, programming, structure or any other aspects of the Services, as well as any term or provision of the Service
Agreement, upon notice to you. If you do not accept a change to the Services, your sole remedy is to terminate the Service Agreement and the Services provided under the Service Agreement, within 30 days of your receipt of our
notice of change to the Services (unless we specify a different notice period), by providing us with advance notice of termination pursuant to Section 31.
So, basically if they want, they can add a charge tomorrow that says you have to pay $1/minute just to have your cell phone ON. Oh, you don't like that? Sure, cancel your plan, $20/month for the remainder of your contract. They can do this and be fully legally justified.
Here is the referenced Section 31:
Unless otherwise permitted by applicable law:
• you may terminate all or any part of your Services upon no less than 30 days advance notice by contacting Rogers at the appropriate points of contact specified in these Terms; and
• Rogers may terminate all or any part of your Services or accounts upon no less than 30 days advance notice to you at your billing address.
Applicable charges continue to apply until the end of the notice period or until the Services are no longer
accessible by you, whichever is later. The transfer of your telephone number to another telecommunications service provider constitutes a termination of the applicable Service(s), and an ECF may apply as set out in Section 8.
And the section 8 they reference:
Unless otherwise set out in the Materials, if you agree to subscribe to one of our plans or Services for a committed period of time (the “Commitment Period”), you may be subject to an early cancellation fee
(“ECF”) for each Service. Any decrease in your Commitment Period may be subject to a fee. If your Service is terminated prior to the end of the Commitment Period, you will pay us an ECF as specified in the Service Agreement, plus taxes.
Check your service agreement, it will say that you are liable for the greater of $100 or $20/month for the remainder of your contract.
*EDIT*
Depending on when you signed there may be a $400 maximum on this charge