if ( condition ) 
{
    get_template_part( \'path/to/template\', \'mobile\' );
}
else
{
    get_template_part( \'template\', \'mobile\' ); // in rootpath
}

// Source in get_template_part
do_action( "get_template_part_{$slug}", $slug, $name );

function wpse21352_template_part_cb( $slug, $name )
{
    switch ( $name ) 
    {
        case \'mobile\' :
            $slug = \'mobile/\'.$slug;
            break;

        case \'tablet\' :
            $slug = \'tablet/\'.$slug;
            break;
    }
    return $slug;
}

// Now attach the above function to get_template_part()
function wpse21352_template_actions()
{
    $wpse21352_mobile_files = array(
         \'header\'
        ,\'logo\'
        ,\'content\'
        // ,\'etc...\'
    );

    foreach ( $wpse21352_mobile_files as $slug )
        add_action( \'wpse21352_template_part_cb\', \'get_template_part_\'.$slug, 10, 2 );
}
add_action( \'after_setup_theme\', \'wpse21352_template_actions\' ); // maybe some other hook