My blackberry used to download at very good speed. Then one day it just slowed so badly to the point where it can't even complete a 1mb download.
At 1st I thought it was because I needed to update my software to OS 7.1. I've done that now and yet my download speed is still slow as ever. I've tried clearing my browsing data and it did nothing for me, battery pop reboot as well and that didn't work either.
There are many many reports on this site from your carrier/region. Some have reported that, when they formally contacted their carrier for support, they were told the problem to be "Network Congestion", but "blame" shifted back and forth between the carrier(s) and RIM. Hence, the only way for this to receive adequate attention and resolution is for everyone who is experiencing it to open a formal support request with their carrier (in your case, MTN according to your profile here).
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.