I've once again gone through the tricky process of setting up a Virgin Mobile Canada prepaid account on an unlocked AT&T iPhone. This time I paid more attention to the contract I signed. It was remarkable what rights I've given Virgin Mobile:
... Unless you decline or withdraw your consent at a later date, you agree that Virgin Mobile, Bell Mobility, Bell Canada, Bell ExpressVu, Bell Media, Bell Aliant, The Source and their affiliates may .... send you communications by any means, including electronically ... products and services of our third party marketing partners;
(b) Telemarketing and Automatic Dialers: Unless you decline or withdraw your consent at a later date, you agree that Virgin Mobile may contact you by phone at your mobile number (and/or at any other contact numbers which you provide from time to time), and using automated dialing and/or announcing devices, to inform you of new offers and promotions, including but not limited to telemarketing messages. If you do not wish to receive such communications or allow the use of your information for these purposes, please call 1-866-580-3625 to change your preferences.
... virginmobile.ca/textalerts for further information or to block premium short code messages.So in addition to paying for these services, we also agree to be spammed, texted, and telemarketed to. If you provide your landline number when asked for contact information  needed to verify the account, then that's fair game for telemarketing as well.
And the carriers wonder why we hate them ... (ok, so they don't wonder.)
 I didn't, and I gave them my Yahoo pure-spam(r) account. But I still need to turn off the texting spam and the telemarketing on the mobile number. Some of this may not be legal in the US, Canada is not famed for consumer protection.