Jibi from The Boy Genius Report expresses his doubts that iPhone can sustain long term growth due to inherent limitations like a lack of third party apps, limited corporate a adoption, etc. The usual complaints.
The Apple iPhone will have early success; Apple and AT&T have all but ensured this fact. It's rare that Apple has failed with any product launch since the re-crowning of Steve Jobs and the first generation iMac. However, Apple has also been known to release rather faulty first generation products that tend to get better in the second and third and beyond generations - they never get it 'right' in the first go-round. Until the next generation iPhone is released, or until third-party application development and porting is opened up to allow integration within the messaging infrastructures of Corporate America, not web-based applications, do not expect to see long-term growth and sales figures to be anything to marvel about (although failed expectations may be mentioned in conversation).