Why can't I text snapchat to verify my number?

I've tried about 2394723 times to text snapchat on my iPhone 4s to verify my number because it is such an effort to manually add people since most of my friends have snapchat.
I thought this could be because my contract didn't allow texts to international numbers (mine is a uk number) but i couldn't get any help on this. Instead I downloaded an app where you can text international numbers. It worked with my American cousin but it still won't send to snapchat! It is really annoying and I just want to get it verified so i don't have to get everyone to remember my username.
So if anyone knows why it doesn't work or has any useful tips/suggestions/answers or maybe another way i can verify my number?, that'd be really helpful

What is snapchat? :/