It's an O2 XDA Ignito, which is an HTC Touch Diamond in a stronger (less placcy) housing. It runs Windows Mobile. I use "Pocket Informant" as the calendar and contacts package - I like that very much: it has some good features, such as colour for different categories of diary event.
I've unscrambled the diary, and I think it's all OK. When I get back to Essex I'll check the "common" items against M's kitchen calendar to be sure.
The SMS facility on the phone stores the name (where known) and number for every message sent or received, so I've recovered a load of names/numbers from there. The call log on the phone bit only records the number, not the name.
I searched the web, and found lots of Forums with folks shouting angrily about ActiveSync and its successor dumping all their contacts details. It's a well-known fact (I now learn!) that it will eagerly delete everything on your mobile device. Several folks had lost their entire business contacts directory - usually after a glitch on their PC that then synchronised their mobile with the (empty) directory on the PC. The instruction to treat the mobile as "master" seems not to work. There was talk of a class action lawsuit against Microsoft, but I don't see that working.
The gruesome truth is that once it's zapped your contacts list, there's no way back unless you have a backup somewhere else.
The consensus of those bitten was: first, NEVER user ActiveSync or Windows Mobile Device Center, and: second, back up with PIM Backup v2.5 (freeware).
I duly downloaded that and saved a backup. I'm not brave enough to test it out by deleting and restoring, but reading it with various text editors and Excel, it seems to have everything there. I could recover contacts from it with no problem; dates are stored in a format that Notepad and Excel don't recognise but maybe the Calendar utility will. I may find out some day.