After months of no answers I bought an iPad and started trying to print postage from it from eBay. I had to use browser instead of eBay app, I had to get an app for my printer, I had to click PRINT POSTAGE on item sold and then touch image of the postage on screen and SAVE IMAGE to photos. I then rotated it since I use labels and then open printer app and select 5x7 and the photo of postage image and CLICK PRINT or send to printer.
This worked for me using new iPad 2 I bought so am sure it will work on my iPhone
Note: I had to use iPhone app on iPad since I like that version better for my printer.
If no app exists for your printer I am at a loss to help, I will be buying an air printer instead of my wifi one soon.
If this helps in anyway or makes someone explore a method that works I will be glad and please share your methods so we all do not boot up gaming rigs just to send packages lol. Hope it helps