LittleToe,
It would be an impossible task for me to prove that all Christians spoke in tongues back then, and I really do not wish to get into a discussion on the availability of speaking in tongues, on this thread.
I would say that all Christians had/have the ability to speak in tongues.
I believe this because I believe all Christians are given the gift of holy spirit, when they are born again.
Please forgive my crude example, but I look at it like a battery, in a vehicle. The battery is there, it is resident power. But in order for the power to be made manifest, the individual has to put the key in the ignition, step on the petal, and drive the vehicle. I liken speaking in tongues to that. It is a manifestation of the inward presence of the holy spirit.
But what I wanted to stress in my prior post was, that there is no requirement to speak in tongues in order to be born again or saved.
The holy spirit is there to those who believe Romans 10:9, whether or not one speaks in tongues.