Jonathan, what pensa said seems very historically correct and these are just my 2 cents on it...
In the Coptic church,readers/chanters do may deacon roles including reading the gospel. We have one tonsured reader at my church and the priest would have a heart attack if he went to the pulpit and even thought of reading the gospel. Actually, the very area of the pulpit and area right in front of the altar is completely out of bounds for anyone under the role of deacon.
Eastern Orthodox altar boys dress as subdeacons but never deacons (ie. they wear the stole coming down both shoulders- whereas ordained deacons wear the stole hanging down one shoulder in the front and the back as I've seen coptic readers/chanters wear interchangeably).
Technically I'm not supposed to read the epistle, but being the altar server, the bishop realizes that if a parish doesn't have a tonsured reader/sub deacon, the epistle still must be read, so the task is given to the altar boy. In some cases, when the altar boys are too young or for whatever reason could not read the epistle, the task was given to a young lady with a clear, loud voice, who was dressed in a black rasso (ie. black flowing outer "church garment" and sometimes a veil), she read the epistle- which of course at first scandalized some of the people.
As for what altar servers do, they light the oil and wax candles, light the censer, cut the bread (in coptic parishes I've seen the priest cut the bread as he's giving it to the people at the end of liturgy-to make it easier, most Eastern Orthodox priests have the bread cut during the matins service (orthros) by an altar boy, usher, or lady of the church society (philoptochos). During the liturgy, the altar boys stand around the altar and pass things like the censer to the priest, and walk around the church during processions with the cross, icons, fans, censer, candles. Also, when there is a memorial for someone who has passed away, they make sure that the priest gets the names of the people, as well as the donation and offering such as sweetened bread/ sweetened wheat. Of course clean-up time is also part of the altar servers' job.