Phone won't connect to mobile network As of yesterday my phone was okay as I know I had a missed call and checked it on voicemail, but today I noticed that it is showing no signal when there should be one.

The last thing I know I did was to try *#61# to check the voicemail numbers as I was thinking of setting a longer timeout, but I didn't actually change it.

If I go into Additional call settings I get 'Network or SIM card error', but I expect that is linked to the lack of network. However, I wonder if something on the SIM is messed up.

I've turned it off/on a couple of times. Also tried a different SIM from a different service and that worked. It there anything I can try resetting?

It's an htc Tattoo on Android 1.6.
I would bring the phone to your carrier's local store.  If a different SIM card from the same carrier works, then it's possible that your SIM card is damaged or corrupted.  The carrier may need to replace it for you.  Keep in mind that some carriers (or authorized reseller outlets) will charge you for this.