Over The Air generally simmulates the dowloading of the 
application of the application on to the mobile using GPRS
connection.

OTA means Over The Air, which is a concept. The following
are the examples which uses this concept.

OTA provisioning - Means provisioning a mobile handset over
the air using PUSH messages

Firmware Upgrade OTA - Which is used to upgrade or downgrade
the firmware of a device.
   
There is a possibility to have a newer versions of the
applications/ MIDLETS which are already installed in the
device. But the user can download the updated SW and install
it with out going to the service center.