We have recently integrated the Holley DTSD545 meter with PNPSCADA.
You can read it via the RS485 port over external modems or etherpads, or if you want to use the internal Holley modem in Client modem over GPRS, you can do so by creating the Holley modem entity on PNPSCADA for the meter to communicate through. (You don't need to specify a SIM card, although the modem does use it, because the identifier used is the meter serial number and the modem cannot be called over CSD - it purely works over GPRS by the meter connecting to the server)
On the meter side, you must set up the GPRS parameters on the meter to work through Client mode and connect to your PNPSCADA server on port 2225.