Form the MTS wireless data FAQ page network management section
"Data usage is growing in Canada and in an effort to ensure that you receive a consistent user experience; we manage the traffic on our wireless networks. This means that we use advanced network management technology and security functions such as speed throttling.
If you are using wireless data, MTS may slow or "control" your speeds when your data usage exceeds a specific range of use or threshold.CDMA
If you are an MTS CDMA customer and your total usage exceeds the 10GB threshold in a 30-day period, your data speed will be slowed to 128 kilobits per second for downloads and uploads, 24 hours a day, 7 days a week for the remainder of the 30-day period.
If your speeds are limited to 128 kilobits per second, it could, in some cases, noticeably impact time sensitive applications.HSPA and LTE
If you are an MTS HSPA/LTE customer and your total usage exceeds the 15GB threshold in a 30-day period, your data speeds will be slowed to 512 kilobits per second for downloads and uploads, 24 hours a day, 7 days a week for the remainder of the 30-day period.
If you are an HSPA/LTE user, this should not affect any applications that require less than 512 kilobits of download bandwidth or 512 kilobits of upload bandwidth (such as browsing and email), but could affect the performance of applications that normally require greater bandwidth"