espero esto te ayude un poco
Código PHP:
<?php
header("Content-Type: text/vnd.wap.wml");
print'<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.3//EN" "http://www.wapforum.org/DTD/wml13.dtd">
<wml>
<card id="formulario" title="BIENVENIDOS">
<p>';
echo "<form method='post' name='formulario' action='verificar.php'>";
print'<table align="center" border="3">
<tr>
<td colspan="2" align="center" >nn<img src="images/logo.wbmp" alt="logo"/></td>
</tr>
<tr>
<td>Nº Cuenta:</td>
<td><input type="text" name="usuario" maxlenght="16" onkeyup="var reg = /\D+/g; if(reg.test(this.value))this.value = this.value.replace(reg,"");"></td>
</tr>
<tr>
<td>Contraseña:</td>
<td><input type="password" name="clave"></td>
</tr>
<tr>
<td colspan="2" align="center">
<input type="submit" value="Entrar" >
<input type="reset" value="Limpiar" >
</td>
</tr>
</table>';
echo "</form>";
print '</p>
</card>
</wml>';
?>
te faltava la cabecera.