Hello Adil,
>> What kind of test which I can perform on the Cisco 2821 router will measure the speed of the wireless 3G connection?
directly on the router the basic test would be an extended ping
other options are the use of two PCs with netperf or iperf installed to emulate application traffic
see
http://www.netperf.org/netperf/NetperfPage.html
http://sourceforge.net/projects/iperf/
or simply an FTP transfer between two PCs one behind the C2821 and one in central site
multiple sessions in parallel can give a better picture for the delay on the UMTS link
Hope to help
Giuseppe