Can I use the Landis and Gyr internal GPRS modem communication module with Plug and Play Scada?

Yes.
If you have your own Plug and Play Scada server, with access to your private GPRS APN TCP/IP subnet, you can use the GPRS modem module in APN mode. When you do this, add the modem in Plug and Play Scada as a Generic APN Modem, where you specify the IP and Port where the server can access the meter.
However, if you don't have an APN or can't use the APN for some reason, you can alternatively use the GPRS modem in active mode. In this case you can also use the modem with any of our public Plug and Play Scada servers hosted by us on the internet.
The way to do this, is first to add an 'Always Connected Generic Active GPRS Modem' in Plug and Play Scada (except for the P42 modem add it as an IPT modem instead - see post below). At this time, a unique TCP Port on the Plug and Play Scada server will be allocated to the modem. Make a note of this port.

The way you set up the Landys and Gyr comms module, is by setting its IP to be dynamic, using the meter programming software (MAP110 or MAP120).
Once you have done this, another field will be available, called the IP Address Central Station. This must be the IP of your Plug and Play Scada server. To get the IP of your Plug and Play Scada server, ping the domain you use in your Web Browser to browse your server, e.g. sdg.pnpscada.com is at the time of writing equal to 196.22.139.148. Please note that the TCP Port setting is the TCP port on the server to which the modem will connect.
There are other settings that need to be set to enable GPRS operation on the modem in general. If the yellow LED on the modem doesn't double-flicker, it is not connected on GPRS. If it is long flashing, you don't have any signal at all. 1 Quick flash at a time means there are GSM signal, but it is not connected on GPRS. When it give a double flicker, you can know for sure it is logged in to GPRS successfully.
So before you even worry about any of the IP or port settings, or any of the settings on Plug and Play Scada, you must first get GPRS working from your modem, otherwise you are wasting your time. To get that working is beyond the scope of this post - refer to the Landis and Gyr documentation, or get support from Landis and Gyr.

There are now multiple versions of Landis and Gyr internal modems, and they have different features, especially as it pertains to configuring it as an Active GPRS modem.
The above post works for the modem that does not have IPT settings. The connection it makes is mapped straight to the meter, and it tries to connect something like every 10 minutes.
We got IPT working for the P42. We can get IPT working on it straight into PNPSCADA, like we've done for the Itron Sparklet modem and the SyM2 modems. By the way, the port on PNPSCADA for IPT is the standard TCP port 7259
Update 2015-01-16
Yes! We just got a CU-P42 Landis modem working with PNPSCADA using IPT! So to get that working, just configure your meter through an IPT Modem entity on PNPSCADA. The User Name (Account id) of the modem must be the same as the meter serial number, and the modem in the meter must be set up to provide the serial number of the meter as the User Name.

(Some old versions cannot do GPRS, or can only do GPRS and CSD alternately, e.g. if you set it according to a schedule, you can get it on GPRS from midnight to 3am and then on CSD from 3 am to midnight)

For the modem that can connect out, see this setup (PLEASE NOTE, THIS IS THE P32, to be configured as a Generic Active GPRS Modem on pnpscada):

TO CONFIGURE THE P42, YOU NEED TO SELECT THESE THREE (3) OPTIONS ON MAP120:

first one:    IP Address Mode  must be dynamic IP address (IPT DIN)

second one:   TCP Port  must be   7259

third one:    IP Address Central Station    must be  

make sure the settings is right by closing it and reading from scratch again after programming it

On PNPSCADA you must add the IPT modem entity, not the generic active GPRS modem! for the IPT modem on pnpscada, the 'Account name:' field of the modem entity must be the meter serial number. That is the name by which the modem identifies itself to the server over IP-Telemetry.

To set the APN name to 'internet'
go to Access Point Name
and set  the Request to +CGDCONT=1,'IP','internet'

Alive Mode is not available with the new P-42 modems

P42 IPT:
make the IPT User Name the same as the meter serial,
and add the modem on PNPSCADA as IPT GPRS modem with Account Name same as meter serial

I think the new P42 modems can be set up as IPT modems.

I have seen people using it with E460s, installed and powered external to a meter, but then to program the modem, it first has to be inserted into a ZMD, and then programmed properly, and then you can install and power it externally.