***edit***
The file path on your phone would be:
sd:/Android/data/com.eamobile.nbajam_sxperia_wf/res
I'll give a quick rundown of the important files:
1.NBAJAM_Players_CONSOLE.csv-This can be opened via Excel or any other spreadsheet program. It acts as the player/roster database file. Here you can edit ratings, assign teams, textures, and animation info.
2.NBAJAM_Players_Teams_CONSOLE.csv-This can be opened via Excel as well. This acts as the team database file. Team ID, info, court assignment, ect.
The rest of the files have generic extensions, but are accessible using either notepad or an archive program such as winrar or 7zip. Navigate to the files in the program or rename the file to filename.zip
3.0 file-Can be opened using notepad. Seems to act as a listing of the assets used by the game.
4.a file-Can be opened in winrar. An archive containing audio for the game. Audio is in .caf format
5.g file-An archive containing player texture file, opened using winrar. Textures are in .pvr format
6.ga file-An archive containing animation files, open via winrar as well. Animations are in .anim format.
7.i file-Opened using winrar. An archive containing menu art and animation files, loading screens, as well as player portraits. loading screens and portraits are in .png format.
These were done editing the NBAJAM_Players_CONSOLE.csv. I added players back into the roster, perhaps removed after an update because the texture files remained. I put Lebron back on cleveland by assigning his textures to Jamison.

Tmac

AI & Yao

Lebron & Varejeo reunion
The textures are in .pvr format which is compressed .png I believe. They can be decompressed using PVRTexTool, found here:
http://www.imgtec.com/powervr/insider/powervr-pvrtextool.asp
I have been able to extract and edit the textures, but have not successfully reinserted them into the game. This is what I got so far:

This is where I'm stuck, testing different encoding options within the program and hoping to get lucky. Lol So close.