Php form auto submit

I like writting in PHP but have alot to learn. I want to have a form have just one field and that I type into and when it after getting to about 150 characters I want to automatically send that to email or cell phone text message and then automatically, seamlessly without having to click any buttons on any page start the form entry again without having to stop typing and have it send the next 150 character and do this over and over util I stop typing. There has to be a way. I thought I had it working but when I sent it to the email page it just kept loading over and over again and next got the email sent. Please help, It seems so simple, just one field, type continuously with no submit button and when it gets to a certain length of message have it send to my cell phone or email. Why is this so hard? HELP!