• Can the XBee 802.15.4 OEM modules talk each other directly? Yes. They can send packets directly to any of their brothers which are in range.

• Can the XBee ZB modules talk each other directly? No. The sensor motes can not talk each other directly. They have to do it through a router or coordinator device. One node acting as a coordinator has to be set so that the nodes can join the network.

• Can the XBee Znet 2.5 modules talk each other directly? No. The sensor motes can not talk each other directly. They have to do it through a router or coordinator device. One node acting as a coordinator has to be set so that the nodes can join the network.

• Can the XBee 802.15.4 OEM live with batteries? Yes. The point here is to find a synchronization algorithm which makes all of them send and receive at the same time. The DigiMesh protocol which can be configured over thos modules uses its own time synchronization algorithm for this purpose.
  

• Can the XBee ZB nodes live with batteries? Not all, at least the routers and the coordinator must be plug powered. The end devices can be battery powered.

• Can the XBee ZNet 2.5 nodes live with batteries? Not all, at least the routers and the coordinator must be plug powered. The end devices can be battery powered.

• Can the DigiMesh nodes live with batteries? Yes. The count with a synchronization algorithm which makes all of them send and receive at the same time.
  

• Can the XBee 802.15.4 OEM and the XBee ZB / XBee Znet 2.5 modules communicate between them? No, as pointed before they use different kind of communication methologies. The 802.15.4 OEM modules rely on the direct communication (point to point), however the ZB and ZNet 2.5 modules use the routes to forward the data to the destination.

• Can I get the DigiMesh protocol running on a XBee 802.15.4 OEM module? Yes, you can choose between using the point to point communication paradigm or set the completely distributed mesh algorithm from Digi. Both protocols use the Freescale chipset.
  

• Can I get the DigiMesh protocol running on a XBee ZB module or XBee ZNet 2.5? No, DigiMesh rely on the Freescale's chipset and ZB does on the Ember's one.

• Can I get the 802.15.4 raw stack running on the XBee ZB (ZigBee) or XBee ZNet 2.5 module? No, 802.15.4 raw stack rely on the Freescale's chipset and ZB and ZNet 2.5 do on the Ember's one.

• Can I get the ZigBee stack (ZB or ZNet 2.5) running on the XBee 802.15.4 OEM module? No, XBee 802.15.4 OEM module rely on the Freescale's chipset and ZigBee (ZB and ZNet 2.5) does on the Ember's one.

• Can the XBee ZB and the XBee ZNet 2.5 modules communicate between them? No, they have a different ZigBee stack. The XBee ZB ZigBee stack implements the ZigBee-Pro v2007 standard and the XBee ZNet2.5 the propietary Ember's ZigBee stack. for this reason Libelium has chosen the XBee ZB (ZigBee-Pro standar) for its sensor devices Waspmote, when a ZigBee configuration is required.
  

• Can I get the XBee ZB ZigBee stack running on the XBee ZNet 2.5 module? Yes, both modules rely on the Ember's chipset and you can choose the configration you want.

• Can I get the XBee Znet 2.5 ZigBee stack running on the XBee ZB module? Yes, both modules rely on the Ember's chipset and you can choose the configration you want.

For more information about 802.15.4 and ZigBee read the 802.15.4. vs ZigBee article.