Sony Ericsson K300

Since this an 850 phone, will this phone be used onCingular or will T-Mob have the phone on their system? Either way this looks like a decent entry level camera phone, just not to sure why SE hasnt made a good quadband phone yet.

I really don´t understand something...I love Sony Ericsson phones but why cant they make one quad-band phone...i wish that they will make one an i would def. buy it...