An official announcement from JYP Entertainment has been released via Wondergirlsworld.com:

JYP Entertainment has announced that Mimi from the Wonder Girls has decided to postpone her musical career to pursue an academic career. Mimi, the rest of the Wonder Girls members, her family, and JYP Entertainment have collectively decided to postpone her musical career for the time being. JYP Entertainment said, "Mimi had a truly memorable, once in a lifetime experience while living in the U.S. and touring over 50 cities. We support her decision to pursue an academic career at this time. We will also support Mimi if she chooses to return to singing after her academics are complete. In the meantime, she plans to frequent JYP facilities and continue her dance and vocal classes." Mimi will remain with the Wonder Girls in the U.S., continuing with any scheduled performances and activities until the end of February. As of March, she will return to Korea and prepare to focus on her studies. JYP has named 17 year old Lim as the newest member to the quintet. Lim has gone through extensive training at the JYP Academy for three years and is fluent in four languages: English, Korean, Mandarin and Cantonese.

Best wishes to Mimi and welcome to Lim! Lim was recently spotted in a dance clip and rumored to debut through the "Chinese Wonder Girls," but that no longer applies! http://www.youtube.com/watch?v=-SA4mg1jshs