While I was dejunking a spare room, I found a few old phones in a box. Surprisingly, all are still working.

Question 1:
I thought it'd be nice to use the Nokia 6800 for texting only. However, it's rejected every SIM card we have in the house. I'm guessing it's locked to a network?

The phone hadn't been used for at least eight years, so I can't remember which network I used. I have no access to the phone's screen menu because there's nothing but a single message that says "Insert SIM card" and when a card's inserted, "Rejecting SIM card". How do I get the phone to reveal the network's ID?

Question 2:
Nokia 9110, T-Mobile Sidekick Slide and Blackberry 7730 are still working. I'd like to donate those to a charity that recycles old phones. Is there one you could recommend?

Thanks for any help.

What networks have you tried so far?

Sorry for forgetting to mention that.

Three, Vodaphone, Orange, O2 and T-Mobile.

I know it's not Virgin because I've never used their services.

It may be that it is having trouble with modern 3G sim cards. I would expect it to say something like Enter Unlock Code if it was locked.

That makes sense, actually. There is a free unlocker for this model of phone here http://unlock.nokiafree.org/ but it seems to need to know what network the phone is locked to, so it would be chicken and egg

Nope. Old Nokias do not work like that.

So what in your "expert" opinion is the problem??

In my "expert" opinion, there is no problem. The OP was correct all along.