The Sony Ericsson c902 cybershot is a great phone, it offers most of the capabilities of a normal Sony Ericsson Walkman phone, except it technically has a different player to the Walkman. It is a 5.0 MP camera/ video recorder which takes good quality pictures and videos, and as with most Sony Ericsson's has a great sound system with good volume.
For me on Vodafone, the signal quality was great and I almost always seemed to have signal. The screen is an ok size at 2.2 inches, and is quite good quality. It also has onscreen touch buttons that work when the phone is in cybershot mode. The phone can hold up to an 8GB m2 memory card that can be taken out and put back in while the phone is on, as it isn't under the battery.
The music player allows you to have lots of playlists, and although the original memory of the phone only allows you to store a few songs, by adding in a memory card, you can increase the amount of songs that can be stored on the phone. It can also store and play .mp4 files, so films can be added and watched, although the screen is quite small.
The battery life of the phone is very good, and usually will last 2 days of use, that include using it as an MP3 player and video player, although using these functions does impact quite a lot on the battery life.
However because of the Sony Ericsson charger, I find that after a while of listening to music on the phone, and charging it, the connecting cable can start to come loose, and will no longer charge the phone.