Talk is great but I know many here in the UK who don't use the phone for talk, just SMS. I used to be one of them! As a teenager on a PAYG phone voice seemed too pricey. The per message charging for SMS was preferred than the per minute for voice. You knew exactly what a text was going to cost as opposed to a phone call that could drag on. Usually we would spend more on texting back and forth than the phone call would have cost but we still did it because of the consistency.

There are plenty of places to innovate even with voice. Theres no mobile white pages (those great big hulking phone books that contain all of the phone numbers of people living nearby) for example. Voicemail and other forms of asyncronus voice are ripe for improvement. Possibly even a 'voice twitter' that would let you record 60 second snippets of audio and broadcast them over website, skype, MMS etc. Micro-podcasting as it were!

Like you, I'm sure voice phone calls will remain the predominant use for a phone but that doesnt stop us innovating with mobile!