<a href="#" class="btn btn-default" data-toggle="modal" data-target="#modalContact" >Кнопка 1</a>
<form>
<input type="name" placeholder="Ваше имя">
<input type="hidden" value="Наше значение" >
<button type="submit" class="btn btn-primary">Отправить</button>
</form>
<a href="#" class="btn btn-default" data-toggle="modal" data-target="#modalContact" data-info="1">Кнопка 1</a>
<a href="#" class="btn btn-default" data-toggle="modal" data-target="#modalContact" data-info="2">Кнопка 2</a>
<a href="#" class="btn btn-default" data-toggle="modal" data-target="#modalContact" data-info="3">Кнопка 3</a>
<a href="#" class="btn btn-default" data-toggle="modal" data-target="#modalContact" data-info="4">Кнопка 4</a>$('.btn').click(function() {
$('[type="hidden"]').val($(this).data('info'));
});