As I understand it, in theory if I write a Midlet that works on my 7210, it should work on all other Series 40 devices (with the same amount of spare memory), like the 7250, 6610 etc?
Does anyone have any practical experience to back this up?
I have tested my Series 40 midlets on several announced and unannounced models. They all work nicely.
In general, the Series 40 phones should work the same as they have the same UI (that's what Series 40 is all about). If I remember correctly, only Nokia 6800 has slightly extended Java feature set. All the other ones should have the same basic CLDC/MIDP firmware.
The same holds mostly true for the other series as well, like Series 30 and Series 60.