What is the difference between the Iridium 9555 and its predecessor, the Iridium 9505A?

The Iridium 9555 satellite phone is smaller and lighter than the Iridium 9505A and also has a more user friendly sleek design and intuitive menu-driven interface an older model. New features make it even easier to use, including an integrated speakerphone, brighter display screen, improved SMS and email capabilities, easier navigation and flexible menu choices through the use of soft keys, an internally stowed antenna and an integrated Mini-USB data port. The 9500 model is the oldest model Iridium phone and a 50 minute pre-paid purchase is required.