To get different upgrades and to level up quicker in the game buy Investments. The Investments feature is found at the 'Exotics' menu, before you go there though make sure you've got at least $1.5 million Dollars.

Montana Holdings:
Fronts cost you 10% less to purchase.

Montana Fitness:
Your henchmen ALL gain 50% health.

Montana Sports:
Maximum bets on gambling increases.

Montana Financial:
0% interest when laundering ALL your cash.

Montana Defense:
Carry an extra weapon and have maximum ammunition.

Montana Records:
Music tracks are unlocked and new playlists created.

Montana Productions:
Tony's clothing options in the cheat menu are unlocked.

Montana Legal:
Visibility Events reduced by half (Police ignore you).

Pause gameplay and select the 'Cheats' option and then enter the desired mission code so the mission is unlocked when you have completed your current mission.

Unlock Deliver Mission:
Enter S12 as a code.

Unlock Un-Load Mission:
Enter S11 as a code.

Unlock The Dock Boss Mission:
Enter A51 as a code.

Unlock Nacho's Tanker Mission:
Enter S10 as a code.

Unlock Marina Storage Mission
Enter F_M_SHA as a code.

Unlock Nacho Contreras Mission:
Enter S09 as a code.

Unlock Babylon Club Redux Mission:
Enter S13 as a code.

Unlock Freedom Town Redux Mission
Enter S07A as a code.

Unlock Cabana Cigar/Oakely Drive-In Mission:
Enter DW_FRON as a code.

Before doing this 'Save' the game then go into the ocean and swim away from land and a giant shark will suddenly appear and eat Tony Montana.

The following codes are entered by pausing game play and entering them at the 'Cheats' menu.

Fill Ammo: AMMO

Fill Health: MEDIK

Unlock 1,000 Balls: FPATCH

Unlock Antique Racer: OLDFAST

Unlock Bacinari: 666999

Unlock Bulldozer: DOZER

Change Time of Day: MARTHA

Unlock Dumptruck: DUMPER

Unlock Lightning: SHAZAAM

Unlock Rain: RAINY

Unlock Stampede: BUMMER

Increase Cop Heat: DONUT

Increase Gang Heat: GOBALLS

Decrease Cop Heat: FLYSTRT

Decrease Gang Heat: NOBALLS

Unlock Grey Suit: GREY

Unlock Sandy Shirt: TANSHRT

Unlock Black Suit: BLACK

Unlock Blue Suit: BLUE

Unlock White Suit: WHITE

Unlock Tiger Shirt: TIGSHRT

Unlock Sandy Shirt with Shades: TANSH

Unlock Tiger Shirt with Shades: TIGERSH

Unlock Grey Suit with Shades: GREYSH

Unlock White Suit with Shades: WHITESH

Unlock Blue Suit with Shades: BLUESH

Unlock BReal 'The World is Yours' music track: TUNEME