A feature being offered on some pagers is the ability to "answer back". A short message could be typed into the pager (via virtual keyboard on screen), then sent back to the party initiating the page. To implement this feature the pager must have a transmitter as well as a receiver; transmit power is typically near 1 watt. This feature is typically implemented on 900 MHz pagers.
The product offering described for receive only pagers would work equally well in the receive side of acknowledge-back pagers, and as the lower power level devices in the transmitter. Products designed for 900 MHz cellular system transmit might also work for the transmit side of an AckBack pager.