i have create a nxt wallet. account id: NXT-3GSC-2MAM-6KBC-2XAQU.
but this coin send message need fee. sending e-mail need no fee.what's nxt coin's advantage?
The importance of arbitrary message is for things like asset exchange and alias registration. Those are actually done via arbitrary message in the background. Since it was already there there was no reason not to go ahead and allow people to use it for sending messages. Its no replacement for email thats for sure but it is usueful for example if you want to contact someone who owns an alias and he hasnt posted any contact information on the internet. Also its useful if you run a business and you want people to be able to contact you but only if its actually important. Other various things.
As for whats the advantage thats a very long and complicated answer but ill try to make it short and simple. Essentially what we have is very good security at low cost on a platform that is as open as possible to new layers of innovation built on top of the core. This doesnt sound like much but its actually a much bigger deal than it sounds. With bitcoin security is actually very very expensive (mostly this cost is born by savers in the form of inflation but not visible due to increasing demand) and in my estimation actually less secure than nxt even with that higher cost. Also its not a very open platform, infact the bitcoin devs have been somewhat non cooperative with the mastercoin devs.