Cheats are entered via mobile phone. Pull it up with the up arrow, (by default) click the up arrow again, enter the cheat, and call it.
Attention - Individual cheats are disabling achievements!

𝐆𝐓𝐀 𝐈𝐕:

ɢᴀᴍᴇᴘʟᴀʏ

Health, add armour, ammo & repair vehicle - 482-555-0100
Refill health, add armour and repair vehicle - 362-555-0100
Advanced weapons set - 486-555-0100
Poor weapons set - 486-555-0150
The police will stop chasing you - 267-555-0100
Adds one wanted star - 267-555-0150
Changes the weather - 468-555-0100

ᴠᴇʜɪᴄʟᴇ sᴘᴀᴡɴ

SuperGT - 227-555-0168
Turismo - 227-555-0147
Comet - 227-555-0175
Cognoscenti - 227-555-0142
FIB Buffalo - 227-555-0100

ʙɪᴋᴇs

NRG-900 - 625-555-0100
Sanchez - 625-555-0150

ᴡᴀᴛᴇʀ & sᴋʏ

Jetmax (boat) - 938-555-0100
Annihilator (heli) - 359-555-0100

𝐓𝐁𝐎𝐆𝐓:

ᴠᴇʜɪᴄʟᴇs

Bullet GT - 227-555-9666
APC tank - 272-555-8265

ʙɪᴋᴇs

Akuma - 625-555-0200
Vader - 625-555-3273

ᴡᴀᴛᴇʀ & sᴋʏ

Floater (boat) - 938-555-0150
Parachute - 359-555-7272

𝐓𝐋𝐀𝐃:

ᴠᴇʜɪᴄʟᴇs

Slamvan - 826-555-0100
Gang Burrito - 826-555-0150

ʙɪᴋᴇs

Hexer - 245-555-0150
Innovation - 245-555-0100
Double T Custom - 245-555-0125
Hakuchou Custom - 245-555-0199