From Forum Nokia Wiki

The Display.vibrate() does not work on some (most? all?) Series60 devices. There are several threads in the forum about this. I can confirm that vibrate does not work on my Series60 3rd edition FP1 6290 phone. The same code runs perfectly on a low cost series40v2 6021 phone. This wiki article should give the developers some more information about these problems, which phones have problem, and if there is a workaround.