T-mobile US highly restricts java applications, especially on their Nokia handsets. With my previous phone, the Nokia 6133, you could flash to an unbranded firmware and run anything. It was great. But now I have a Nokia 6086 ...
The Nokia 6086 has many certificates installed on it. Go to Menu > Settings > Security > Authority certificates > Certificate list to view them.
One certificate of interest is GeoTrust CA for UTI. UTI is Unified Testing Initiative, or Java Verified. This is the certificate real applications will get, such as Google Mobile Maps.
If you visit http://m.google.com/gmm you'll be presented with a download link, and then a popup saying something about the application not being trusted. Do not download, but instead clear your cache with Options > Other Options > Clear the cache. Then Options > Reload. Repeat until the download does not warn about the application being from an untrusted source. I was told you may have to try "like 18 times" but I believe that since I cleared my cache, it worked the 1st reload.
That's it. Congratuations, you can now use Google Maps, because they make available a signed application. Applications MUST be signed to gain access to network functions. Trust me, there is no other workaround, and getting your own application to work requires you to pay $300/yr at least to get it signed by one of the companies whose certificate is included on this handset.
Of course I also suggest Opera Mini. Just visit that site and it's been signed by multiple certs now (I see Thawte showing up for me) and should work no problem! I'm so happy they finally have decided to include this as it really really helps out us poor guys stuck with crippled T-Mobile handsets! Thanks, Opera, luv ya! :)