I don’t think that is so odd - not with programmable phones. You enter the number once then just hit their name to call - don’t forget she had just started dating Tony a few weeks before this - so texting and calls were all done by his name, not number. She didn’t have her phone any longer and was having to dial the number from the jail phone.
My husband has no clue what his, mine or my 3 sons cell numbers are. All he knows to do is press a button. :)
Casey Anthony’s Cellphone Usage in the Thirty-one Days that her Child was “MISSING”:
http://www.acandyrose.com/casey_anthony_31days.htm