Help with a simple contact form

General information for the website: Contact Form
Description of requirements/features: I have been experimenting with HTML5 and CSS3, as well as PHP and JS to create a very simple contact form, take a look here: loaistudio.com/contact

Everything seems to be working fine, however I believe there is a better way to do the contact form and to improve it, make it more secure as well as reliable.

So I am seeking someone's help whom experienced at PHP and JS.
I have posted the current code of the form here if you wish to have a initial look: http://codereview.stackexchange.com/questions/39103/how-to-improve-this-current-contact-form/39118?noredirect=1#39118

Again, it is a very simple form. I just need help to improve it and make it simpler as well as secure and reliable. Please note this form is a Template, and I want to be able to add more fields later on, so don't lock everything for 3 fields like you see now on the form.

Ideas: Can we get rid of JS and make the form run using PHP? can we still validate it and show a thank you message as well as a custom errors?

You don't really have to do everything alone, again I am a developer but not that experienced.

Thanks.
Leo
Extra notes: I have been experimenting with HTML5 and CSS3, as well as PHP and JS to create a very simple contact form, take a look here: loaistudio.com/contact

Everything seems to be working fine, however I believe there is a better way to do the contact form and to improve it, make it more secure as well as reliable.

So I am seeking someone's help whom experienced at PHP and JS.
I have posted the current code of the form here if you wish to have a initial look: http://codereview.stackexchange.com/questions/39103/how-to-improve-this-current-contact-form/39118?noredirect=1#39118

Again, it is a very simple form. I just need help to improve it and make it simpler as well as secure and reliable. Please note this form is a Template, and I want to be able to add more fields later on, so don't lock everything for 3 fields like you see now on the form.

Ideas: Can we get rid of JS and make the form run using PHP? can we still validate it and show a thank you message as well as a custom errors?

You don't really have to do everything alone, again I am a developer but not that experienced.

Thanks.
Leo