These unlockables are accomplished by doing various in game tasks:

2K4 Team: 
Record 15 double-doubles to unlock the 2K4 team 

ABA Ball: 
Play in 1 street mode game to unlock the ABA ball 

All Atlantic Retros: 
Record 5 wins with any Atlantic division team to unlock all Atlantic retro jerseys. 

All Central Retros: 
Record 5 wins with any Central division team to unlock all Central retro jerseys. 

All Midwest Retros: 
Record 5 wins with any Midwest division team to unlock all Midwest retro jerseys. 

All Pacific Retros: 
Record 5 wins with any Pacific division team to unlock all Pacific retro jerseys. 

All-time 76ers: 
Grab a total of 150 rebounds to unlock the All-Time 76ers team 

All-time Celtics: 
Block a total of 100 shots to unlock the All-Time Celtics team 

All-time Lakers: 
Steal the ball a total of 20 times to unlock the All-Time Lakers team 

All-time Sonics: 
Dish out a total of 150 assists to unlock the All-Time Sonics team 

Bonus Street Court: 
Play in 20 street mode games to unlock a bonus street court 

Boss #1 court playable in street mode: 
Defeat the 1st 24/7 boss to unlock his court in street mode 

Boss #2 court playable in street mode: 
Defeat the 2nd 24/7 boss to unlock his court in street mode 

Boss #3 court playable in street mode: 
Defeat the 3rd 24/7 boss to unlock his court in street mode 

ESPN Ball: 
Play in 5 street mode games to unlock the ESPN ball 

Exploding ball: 
Attain 50% unlockables completion to unlock the exploding ball in street games 

Hall of Fame difficulty mode: 
Attain 100% unlockables to unlock Hall Of Fame difficulty mode 

Menu color 1: 
Start a franchise mode game to unlock hidden menu color #1 

Menu color 2: 
Finish a franchise mode season to unlock hidden menu color #2 

Menu color 3: 
Finish and win the championship in franchise mode to unlock hidden menu color #3 

Menu color 4: 
Complete 15 years of franchise mode to unlock hidden menu color #4 

Menu color 5: 
Complete 30 years of franchise mode to unlock hidden menu color #5 

Menu music 1: 
Start a season mode game to unlock hidden menu album #1 

Menu music 2: 
Win the championship in a 14 game season to unlock hidden menu album #2 

Menu music 3: 
Win the championship in a 28 game season to unlock hidden menu album #3 

Menu music 4: 
Win the championship in a 56 game season to unlock hidden menu album #4 

Menu music 5: 
Win the championship in a 82 game season to unlock hidden menu album #5 

Ooga Booga Ball: 
Play in 15 street mode games to unlock the Ooga Booga Ball 

Rock Ball: 
Play in 10 street mode games to unlock the Rock Ball 

Rookie Class: 
Score a total of 100 points to unlock the Rookie team 

SEGA Sports Challenge Team: 
Record 1 exhibition game win to unlock the SEGA Challenge team 

SEGA Team: 
Play for 10 hours total to unlock the SEGA Team 

Sophomore Class: 
Score a total of 500 points to unlock the Sophomore team 

Superstars team: 
Steal the ball a total of 100 times to unlock the Superstars Team 

VC Team: 
Record 15 Triple-doubles to unlock the VC team.

Increase the difficulty of your opponents free throws: 
When playing against a human opponent, while they are at the line push the L trigger repeatedly to cause your opponents controller to vibrate. This increases the difficulty of free throws.

Get all 24/7 unlockables: 
When creating your player for 24/7 First Name: HUNT Last Name: 4TREASURE in all caps.