My 5 year old makes calls as well as answering the phone - 5 is far from being a toddler (I have a toddler too, kids of 5 and 2 years old are pretty much different species :o )
All the kids around here make calls from 4 or 5 years old, to arrange to play - until about 7 the phone gets passed to the parent at some point in the call to confirm arrangements, but with my 7 year old I never have to speak to her friends' parents unless it is a sleep over they're planning. Mobile coverage is very intermittent here, so the land line is the main one in use, and it is generally answered by children in all the houses I call on a regular basis, and that never causes a problem in my experience :)
All the 4 and 5 year olds I know through my 5 year old are very capable of using a phone appropriately, whether answering or making calls under supervision. By 7 children are more than capable of writing down messages too, and of making calls for the purpose of asking friends to clarify homework or school arrangements, and arranging their own play appointments by phone too :)
My kids say our surname when they answer the phone, because that is how everyone here (Germany) answers the phone, then the caller always says who they are, and if they want to speak to somebody other than the person who has answered they state that, and the phone is passed on accordingly, complete with info on who is on the other end of the line.
I'm not getting why kids have to be 8 to manage the conventions of a phone call, even given the OP was being tongue in cheek about 14. Its like many things in life - kids who do something regularly, and under guidance at first and as appropriate, are more than capable of a lot more than some adults give them credit for, at much younger ages.
If a child of 5+ without special needs can't answer the phone properly it is because they haven't been taught how - and it really isn't hard!
It is perfectly possible to stop toddlers answering the phone if you don't want them to though, mine is a tear away at times but the phone is somewhere he can't get it (despite being a spider monkey disguised as a 2 year old) but his older siblings can.
However I absolutely agree with Kitty who said she couldn't give a stuff what the person phoning her house thinks about her kids answering - if you are phoning somebody you usually want something from them, so can't really complain about the quality and age of the "help" on the other end of the line ;)