I'm tempted to get a Mobidapter and use it on my E51 (which is going to be the companion of my future n900, since I have separate sim cards for voice and data). Though, it's quite expensive. And, no used ones on ebay.

EDIT you can get a Mobidapter for about 20 EUR less than Expansys on http://www.roalan.com. Mine is going to cost 40 EUR including VAT and airline shipping.