I am writing a midlet and testing it on Nokia E7-00 and E6-00. A big part of it are Lists, where each item has an image.
When each list item is shown its image is loaded using LWUIT's NetworkManager (which doesn't block the EDT). However while the images are loading the application is almost unresponsive. If I replace the images with static ones there are no performance problems.
I have tested it with the phones being connected to a WiFi network. The devices are not updated to Symbian Anna (I was asked not to make it a requirement unless absolutely necessary). Each list screen shows about 6 items.
The images are jpeg images, 70x70 pixels.