opera mini version 4.1 onwards supports bengali/bangla support even if your phone doesn't support it. It does it via rendering bengali text in the server, rather than on phone, and then displaying. Thus opera mini enables older phones which don't support bengali natively. 

to enable bengali support, type in "opera:config" in your operamini address bar, without the quotation marks, you will be taken to advanced configuration page. change 'render complex scripts" on 'phone to 'server'. Now you will be able to use opera mini to see bengali unicode text. This actually can be useful to see any unicode supported complex script text like Hindi, tamil, kanara