the problem i find is that being self employed i have to think at least 2 months ahead ,pay days are eratic especially nowadays and being commited to even small DD's can be a bind on cashflow so i prefer to pay online /over the phone as much as possible even if it means being ahead as and when the money comes in ,i would count that as my 'buffer' but as mentioned with VMobile it is a requirement of the contract to have a DD even though mine has never been used because i'm always at least a month in credit ,they will still cut me off if i cancel the DD ,incidently it's the same for VM's 30 day rolling contract on payg .As i said earlier i don't see the point in insisting on DD because it's not a guarantee of payment