I'm going 16gb, regardless of price...
1. With iTunes Match I now store very little music on my phone itself now.
2. I don't keep photos on my phone, other than the camera roll between syncs.
3. I don't store video on my phone.
4. A lot of the incremental cost for the bigger capacities is eroded at re-sale time.
I have a Blackberry as work abroad a lot and BBM is the cheapest way to communicate with home as uses wi-fi.
Can Messages on the iPhone link to an iPod Touch and therefore do the same?