It looks like that Nokia is going to announce two new low-end Lumia Windows Phone 8 handsets at Mobile World Congress event this month. Two new unannounced Nokia handsets Lumia 720 (RM-885) and Lumia 520 (RM-914) have passed the certification in Indonesia.
Nokianesia have got some internal documents from Directorate Post & Telecommunication Indonesia, which shows that two unannounced Nokia handsets Lumia 720 and Lumia 520 have already passed the certification from Indonesia Telecommunication on 06, 2013. The leaked handsets appears to be WP8 successor of the Lumia 710 and Lumia 510 respectively.
Both of the handsets are expected to be revealed in Barcelona at the Mobile World Congress event later this month, along with other rumored high-end handsets.
[Thanks to @nokianesia for the Tip]