Just like to make a point on the cellphone idea.

After the bombings in London, the ambulance authority requested the general public to "program" their cellphones with an "ICE" number, In Case of Emergency. Gives names and numbers of people to contact. List all contacts ICE1, ICE2 etc.
Now if your are going to loan a cellphone to your child and/or babysitter then, no one has to remember any specific name or number just look up ICE.

This maybe old news, but it's what sprang to mind when reading this thread and the subject of phones.