Anil de Mello wrote a Latency Tester program for the J2ME platform (which means that Java enables phones should be able to use it). The test results are posted to the web as well as displayed on the screen but unfortunately they are not cached locally (maybe a good thing) but if I did want to refer back to them I had to re-run the test (small point I know).

The JAR/JAD files can be found here.