The Sony Ericsson T310 is a feature-rich phone loaded with every thing that one would want in a phone and at the same time friendly on the pocket. The latest to be launched in the range of sony Ericsson phones is the T230 which is also light on the pocket.
Now there are some differences in these two handsets so you can pick and choose depending on your requirements and preferences. The T310 is a triband phone and has infrared connectivity both of which are missing in the T230 while at the same time the dispay of the T230 supports 4096 colours and is clearer and better than that of the T310 which supports 256 colours. The response time of the T230 is also slightly better than the T310 and it has a better cosmetic design.
Both the phones have the ability of attaching a camera that can be purchased separately.
for more information on the T230 you can check out this website
https://imobile.com.au/Future/default.asp?ID=futureoct0302
All in all I would say that for the frequent traveller abroad the T310 would be a better option since it has triband operational capability but for a normal user looking for a good, solid phone, the T230 is definitely a better option. Also keep in mind that the T230 is the latest in the range of sony Ericsson phones.