Verificar o Estado pelo Cep.

estado.php

public function getEstado($cep)
{
    $estados = array('ac'=>'69900,69999',
                     'al'=>'57000,57999',
                     'am'=>'69000,69299|69400,69899',
                     'ap'=>'68900,68999',
                     'ba'=>'40000,48999',
                     'ce'=>'60000,63999',
                     'df'=>'70000,72799|73000,73699',
                     'es'=>'29000,29999',
                     'go'=>'72800,72999|73700,76799',
                     'ma'=>'65000,65999',
                     'mg'=>'30000,39999',
                     'ms'=>'79000,79999',
                     'mt'=>'78000,78899',
                     'pa'=>'66000,68899',
                     'pb'=>'58000,58999',
                     'pe'=>'50000,56999',
                     'pi'=>'64000,64999',
                     'pr'=>'80000,87999',
                     'rj'=>'20000,28999',
                     'rn'=>'59000,59999',
                     'ro'=>'76800,76999',
                     'rr'=>'69300,69399',
                     'rs'=>'90000,99999',
                     'sc'=>'88000,89999',
                     'se'=>'49000,49999',
                     'sp'=>'01000,19999',
                     'to'=>'77000,77999'
                    );

    $comparar = str_split($cep, 5);

    $comparar = $comparar[0];

    foreach ($estados as $key => $value) 
    {
        foreach (explode('|',$value) as $valores_cep) 
        {
            $ceps = explode(',',$valores_cep);
            if($comparar >= $ceps[0] && $comparar <= $ceps[1])
            {
                return $key;
            }
        }
    }

    return false;
}