The only way to get rid of the operator logo is if you have a sagem phone data cable. Download the Telmem plus (search google for it) software and do it that way. However if you're Orange (and also Virgin I think) then it's impossible to remove the operator logo because the logo data is stored in the sim card and loads it everytime you turn the phone on whereas with O2 and some other operators it isn't stored on the sim card and so can be changed.
No, it's not possible to download a blank logo.