I had used a pearl 8100 and it was never reliable for me. I never tried the older firmware because it was not an option for me. The tether was stable but actually getting to the internet from my n800 was very hit and miss. Downloading pop email would pull a few emails but never finish successfully. Web browsing would sometimes sort of work if I hit reload often enough for each page.

I then tried a nokia 6263 and everything worked fine. Not the fastest but usable. I am currently using a nokia 6267 and it is working fine also.

T-mobile crippled the 6263 too much for me but that is another story.