Prerequisite for either tester: version 2.4.1.2 or later of the DAHDI-cnet drivers.
This is my own implementation in PHP. Just make sure you have a command-line PHP interpreter installed, copy this into your agi-bin directory (usually /var/lib/asterisk/agi-bin), and add it to your dialplan. This version does not need any audio files or applications beyond what is standard in Asterisk-cnet. It does not play an announcement when it starts; that can be done in your dialplan, if you want it.
August 20, 2011 UPDATE:
cp dspeed.agi /var/lib/asterisk/agi-bin
chmod +x /var/lib/asterisk/agi-bin/dspeed.agi
This is based on Max Parke's dial speed test code. However, instead of using the system log, it uses pulse logs accessable through the /proc filesystem, kept independently for each channel.
Note that you could use either of the dial speed testers. If you use the PHP version, you might want to play back an announcement.
exten => 031,1,NoCDR
exten => 031,n,Answer
exten => 031,n,AGI(dspeed.agi)
exten => 031,n,Hangup