It is possible, but you will be unlikely to increase agreed allowances in this regard. I got a new contract with T-Mobile ( as was -- now EE) during my IVA with no problem.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
Can you stay with your current provider? Shouldn't be a problem if you do.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk