Can a repeater boost the signal to devices operating on different networks simultaneously (i.e. a Sprint phone and a Verizon aircard, etc)?
Yes, as long as the carrier in question operates at a frequency that is supported by your repeater and signal for that carrier is available to boost. Keep in mind that different carriers are likely to be broadcasting from different towers, so you may not see the same signal increase on devices from different carriers – for example, if you are trying to boost the signal to both a Sprint phone and a Verizon phone, the repeater may provide a bigger boost to one simply because that carrier’s tower is closer.