We brought an El Cheapo Woo Flung set of eBay, with 2 IR HD cams. We then brought another 2, to make a 4 cam system.
Connects to internet using a standard network port. Took a bit of jigger-ry poker-ry, to get it going on the mobiles (mainly down to instructiuons looking like they had been fed into google translate, and not read by an english speaker).
Also need to leave the case lid off, or else it overheats, but its up out way, and dust protected.
Cracking system for the £80 we paid, no complaints. Cameras are wired, though.