Unfortunately you can not "reverse transfer" money from your mobile phone account to a mobile bank account.
The reason for this is simply:
$1 airtime does NOT equal $1 cash.
When you buy airtime, you get it from the guy on the street. He is given a commission (usually 8c), whilst he gets it from a distributor who is also given a commission (usually 2c). Further, you normally buy a recharge card, which has costs for it to be manufactured and delivered to you, say 3c, and there is also VAT that is chargeable, say about 10c.
Already looking at that, there is 77c left on the table, and for the mobile network carrier to give you $1 in your mobile wallet will not work. Even though there is about 77c left on the table, the chances are high that you will call with it, using their network and they will bill you and make something out of you.
For them to give you $1, when there's $0.77 left, and the possibility of you spending it elsewhere and NOT on their network, will not do for them.
I doubt even M-Pesa, or Orange Money allow this, but if they can drop the costs of them getting the airtime to the end user and if the merchants that are using their mobile money to sell their items are willing to take the hit, I think it is best for this to be done this way.
But then again, it will be best for the merchants to just enter into an agreement with the MNO to do what is called Carrier Billing.
Hope that helps in answering your question.