Spirit-X

Unlock all the tables for all characters:

This will enable you to get "The Tourist" Achievement (20), and could help you towards "The Collector" (45) achievement. To perform a "soft shot", hold the left button while hitting any spin. To perform a "focus shot", hold the right button while hitting any spin.
Unlock Liu Ping's Table Win a match against the CPU using a soft shot
Unlock Luc's Table Win a match against the CPU using a soft shot
Unlock Solayman's Tables (2) Win a match against the CPU using a "Focus" shot.
Jesper's Shirts and Table

Do the following to unlock Jesper's shirts and table:
3rd Shirt Win a match using a forehand shot
4th Shirt Win a match with a 4 point deficit comeback
5th Shirt Win a match with a slow shot
Table Win a match against Computer using soft shot

Rockstar Table Tennis Cheat Codes:
Use these codes at your own risk, however! The moment you use any cheats, you can't get any achievements for Table Tennis from that point forward under that gamer profile.

Code Entry:
All the codes are entered after you load the map and before you press the button to accept the match. The Up/Down/Left/Right directions are entered on the D-pad. RT and LT mean Right and Left Trigger respectively, and RB and LB refer to the Right and Left Bumper buttons on the top of the controller.

Up, Up, Up, RB, RT, RB, RT Big Crowd Audio
Up, Right, Down, Left, LB, Right, Up, Left, Down, RB Unlock All
Down, Down, Down, LB, LT, LB, LT Small Crowd Audio
Up, Up, Down, Down, Left, Right, Left, Right, LB, RB Vintage Audio
Left, Right, Left, Right, Up, Up, Up, X Big Ball
Up, Down, Y, Y, LB, LT, RT, RB Silhouette Mode
X, Y, X, Y, X, Y, LT, RT, Down, Down, Down Offline Gamertags
RT, Up, Down, LT, Left, Right, Y, X, X, Y Sweaty Character Viewer
Up, Down, X, X, Y, Y Colorblind Spindicator (only in newest patch)
Up, Left, Up, Right, Up, Down, Up, Up, X, X Big Paddles Cheat (only in newest patch)

2 Gamerpics:
To unlock the paddles & Rockstar logo gamerpics complete the training mode and get a perfect.
Paddle Gamerpic - Get perfect in training mode.
Rockstar Logo Gamerpic - Get perfect in training mode.

Bonus Shirts:
Liu Ping Shirt #4 - Win a match with a smash shot
Liu Ping Shirt #5 - Shutout the CPU in a game
Liu Ping Shirt #3 - Have a rally of at least 40 hits

Unlock all characters easily:
To unlock all the characters in Table Tenis you dont need to go through tourniment mode, or even beat the tournments within time limits. An easier way to unlock the characters is to play the CPU a bunch of times. This can be done either in tournament mode or exhibition mode with any settings

Unlock Juergen - 20 wins
Unlock Kumi - 25 wins
Unlock Solayman - 30 wins
Unlock Carmen - 35 wins
Unlock Cassidy - 40 wins
Unlock Jung Soo - 45 wins
Unlock Mark - 50 wins

Achievements:
Complete each achievement to get the allotted gamerscore.

Unlocked Mark (20 points) - Win the Rookie Circuit under the default settings in less than 13.5 minutes.
Unlocked Jung Soo (20 points) - Win the Rookie Circuit under the default settings in less than 14 minutes.
Unlocked Cassidy (20 points) - Win the Rookie Circuit under the default settings in less than 14.5 minutes.
Unlocked Solayman (15 points) - Win the Pro Circuit.
Unlocked Carmen (15 points) - Win the All-Star Circuit.
Unlocked Juergen (5 points) - Win the Amateur Circuit.
Unlocked Kumi (10 points) - Win the Rookie Circuit.
The Creampuff (5) - Beat the Amateur Circuit on default settings.
The Graduate (5) - Earn the highest score on every drill in Training Mode.
The Noob (5) - Complete your first online match in any game mode.
The Spectator (5) - Awarded for spectating in an online match.
The Average Joe (10) - Beat the Rookie Circuit on default settings.
The Victor (10) - Awarded for your first win in any online game mode.
The Competitor (20) - Beat the Pro Circuit on default settings.
The Natural (20) - Use every character to beat any of the Tournament Circuits.
The Tourist (20) - Every level in the game has been unlocked.
The Tailer (25) - Every outfit in the game has been unlocked.
The All-Star (30) - Beat the All-Star Circuit on default settings.
The Owner (30) - Every character in the game has been unlocked.
The Net Veteran (60) - Rack up 10+ hours of online gameplay time.
The Veteran (60) - Rack up 10+ hours of offline gameplay time.
The Savant (80) - Beat the All-Star Circuit with every character.
The Widowmaker (95) - Shutout opponents in 5+ non-consecutive games (any settings) in Ranked online play.
The G.O.A.T. (100) - Achieve the highest TrueSkill rating possible in any Ranked online game mode.
The Hall of Famer (100) - Has won 50+ (non-consecutive) Ranked Tournaments.
3 Match Winning Streak (35) - Win 3 Ranked Exhibition Matches in a row.
4 Match Winning Streak (50) - Win 4 Ranked Exhibition Matches in a row.
5 Match Winning Streak (85) - Win 5 Ranked Exhibition Matches in a row.