I have been using the Scout Guard SG580M for a security application and have been really pleased with it. Placed it out in July and it ran until November really well.
Planned on using it in the deer woods this year but broke my ankle and didn't get to.
There are some units out now that send the mobile pics in 640x480 instead of the 320x240 but have not used one of those personally yet.
The SG580M is basically the same as a SG550 cam but with the wireless added.
What you do is get a sim card from ATT, T-Mobile or Verizon and place it in the cameras. Then you get a text message only plan for the sim card and pay from $15 to $25 a month for the wireless part of the camera. They also still save the full size image to the SD card inside the unit.
Hope this helps you a little.