Yes it is. I have done it before but I can't remember the name of the site I used to do it on! Sorry! BTW - did you know you could text house phones! My boyfriend text "bring me up a drink" to his house number and his mum got all freaked out downstairs, hysterical to listen to!
Try the O2 site
http://www.o2.co.uk/
look on the lefthand side bar
There used to be other sites - including Lycos. Lycos may still work, but I have forgotten my log-in details, it's such a long time since I used it.
The O2 site used to be known as Genie.
No - I've just sent one to myself, and I don't have an O2 address
It's now limited to 30 messages a month, however. It used to be something like 400, I think.
My company uses a program called Red Oxygen.We send out emails to our engineers,which they receive as a text message on their mobiles.If they reply to the message, it comes back to the office as an email.I dont know how it all works, but it is excellent.