You cannot use a CDMA Blackberry as a modem (currently).
The 7250 will respond to Hayes AT commands--so it's obvious that there is indeed a modem built into the device. However, AFAIK, no CDMA carrier has enabled this functionality yet.
There are rumours that the 7250 is upgradeable to EVDO with a forthcoming OS. However, there has been no word on whether or not modem capability will be introduced.