Download FExplorer and install it on your phone.

Applying an oplogo -

1: Send the 97x25 image to the phone. (transparent .png images are not supported).
2: Open Fexplorer and locate the oplogo from where you saved it.
3: Press Options\Properties and then select the "set as oplogo" option.
4: Your phone will auto restart and the new oplogo should then be in place.

Some 7610/6620 owners have reported,that the oplogo switches back after a certain time,this seems to be network specific and there doesnt seem to be any way around this as yet!

Removing an oplogo -

Open Fexplorer and navigate to C:/system/apps/phone/oplogo : delete the oplogo image and restart the phone. (this will only remove previously applied oplogo images,it will not remove the default operator text).