Is There a way of using an alt key on the iphone (to so alt characters)

There is no alt key, so no, but there are a lot of preloaded symbols already on the phone, all you have to do is hold a key and extra options will come up. For example, if you want an accent over a, hold a, and it will give you options for it. This also works with the symbols, for example, the $ symbol can be held to provide the money symbol for euros, yens, pounds, etc.