After using up your data limit, your data should just be significantly throttled instead of cut off completely. So you should still be able to send and receive emails, load web pages, etc. Even on the 150mb data plan you should get an unlimited amount of throttled data after you use up your 150mb. I hate the fact that you could miss important emails if you use up your data cap. Wind already does something similar on their unlimited data plans where you get 5gb at full speed and after you use that up it's throttled, it's too slow to watch videos or download big aps or anything like that but at least it still lets you receive emails and (slowly) load webpages.
If this is not feasible, then how about introducing a new addon for an unlimited amount of throttled data, for those of us who don't need high data speeds but want to make sure we never miss an email. Even if it's severely throttled (eg dial-up speeds from the 1990s) it should still be sufficient for emailing.
