I think some clearification is needed with regards to this 4.0 browser(s) and OTA version.
3 different browsing capabilities which depend on the BB OS Version and what infastructure your on [ 1&2 from older versions ] .
1. WAP Browser ( No BES/MDS ) using carrier WAP Gateway
2. BB Browser - corporate hosted BES/MDS
3. Internet Browser ( new in 4.0 ) - MDS hosted by carrier.
You can't download a .jar file via the WAP browser because the regular midlet needs to be converted to a BB .cod file ( .cod = code ), which can only be done ( for OTA ) via the BES/MDS.
So its not just a matter of updating you BB OS to 4.0 but a function of the entire infrasture being updated as well.
Hopefully that clarifies.