Mobile Money Transfer Now in Uganda 
Once you have enabled your sim card to become MTN Mobile enabled as opposed to sending money to friends and relatives, you can also buy airtime.

Go to MTN Menu> Mobile Money> Buy> MTN Airtime> Amount> 5,000 >Mobile Number>......>Confirm Entry> Ok> MM Pin.....> Confirmation message will follow.

If you have more than 5,000 or 5,000 shillings as balance on your mobile money account, you can use it to buy airtime in case it runs out and yet you were in the middle of an important call with no airtime vendor near by.

It is important to note that you cannot buy airtime below 5,000 as that is the minimum amount to be sent for moblie money transfers.