Sat nav on phones can't touch a standalone unit at the moment. Especially the options for blackberry.
Go for a Garmin system. I have a 205W. Wide screen, UK & ROI mapping. Easy as feck to use, very reliable. Would highly recommend it! TomTom's are all great but I see a lot that I sell come back with issues.
http://www.halfords.com/webapp/wcs/..._productId_498027_langId_-1_categoryId_165685