[Nero_3D]

Its not printf, the problem is that your code crashes due to an array out of bounds error
Next time try the crashdetect plugin which would have told you

In both loops you do

pawn Code:

for(new i; i < sizeof(Contact); i++) // i < MAX_PLAYERS

But you actually wanted to do

pawn Code:

for(new i; i < sizeof(Contact[]); i++) // i < MAX_CONTACTS

So fixed it could look like

pawn Code:

//
    for(new i, text[32] = "None"; i < sizeof Contact[]; i++) {
        Contact[playerid][i][ContactName] = text;
        Contact[playerid][i][ContactNumber] = 0;
    }

pawn Code:

//
    new
        str[MAX_CONTACTS * 38] = "Lisa uus kontakt"
    ;
    for(new i; i < sizeof Contact[]; i++) {
        format(str, sizeof str, "%s\n%s (%d)", str, Contact[playerid][i][ContactName], Contact[playerid][i][ContactNumber]);
    }
    TELEFON_valik[playerid] = 10;
    ShowPlayerDialog(playerid, DIALOG_TELEFON, DIALOG_STYLE_LIST, "Telefon (Kontaktid)", str, "Vali", "Katkesta");