Mobile Phone disposal

Spurred out of inaction by Mrs M at the weekend, I had a huge clear out of my wardrobe and study. I have about 5 or 6 old mobile phones to get rid of. One of the charity bags which dropped through our door the other day listed them as items they'd accept. Now I've taken the batteries and SIM cards out, but is it safe to just let the phones themselves  go this way? I think I read somewhere that there was still a danger of personal information being accessed from them? Any advice for a copmplete technical ignoramus?