Your BlackJack is capable of using different networks and technologies to access the Internet. These high-speed networks include Cingular's 3G (UMTS/HSDPA) network and EDGE/GPRS network .
Though I have found it difficult to get exact numbers, I believe the EDGE network is potentially capable of about 170 Kbps but you will probably get more like 70Kbps to 135kbs in your day to day life. As for the 3G network, HSDPA has a maximum data speed of 14.4Mbps but you certainly will not get this. "Current HSDPA deployments now support 1.8 Mbit/s or 3.6 Mbit/s in downlink." (wikipedia quote). Like on the EDGE network, in the real world you will see slightly less speeds: "In the U.S., it provides average download speeds between 400-700 kilobits per second (kbit/s), with bursts to more than one megabit per second (Mbit/s). deployed." (wikipedia quote).
So what speeds are you getting? Want to know? Point your Internet Explorer at http://dslreports/mspeed/ and find out.
I understand that there may be some "hacks" out there to increase your speeds, and if I get some time I may look them up and report back.