Unis is a Thai brand.
You will find all you need to know here:
http://www.wapzon.com/web/prodetail.asp?Pid=3770
To download ringtones etc. You can do it via
WAP over
GPRS providing you service provider has the revelent settings. (Contact them to find out) and you can find a provider that has content for this phone.
I have played with the u100 and from my limited experecne they apper to be good phones.
I am a little concerned with warranty, so beware if the phone playes up. It might be difficult to get it fixed.
But have a play with it and let me know.
Also: Remember that Japan and Korea now run
3g networks so you might see more of these "Asian" phones appearing in youir area.
These phone do use
sim cards but work only on the
3g network.
Most
3g phone you find will be either network or
sim locked.
Hope it helps.