Solid Green!  Okay, fellow At&t 3G Microcell users with problems, these forums helped me out, so here is my story.  Hopefully it can help someone else. – I got my 3GMC second hand, and for weeks I have been working daily to try to get it activated and working properly.  Problem 1: hooked up using option A= solid power, Ethernet, and gps lights & RED blinking 3G light. Solution: Previous owner had not logged in or called At&t to “disconnect the device from the network” and so it didn’t recognize the gps location as being where the activated user was in the world.  That owner finally disconnected it, and the blinking red 3G light turned blinking green.  I thought, great, now I can activate it online and it’ll just work.  Wrong!  Problem 2: a never ending blinking green 3G light. I scoured the forums, had multiple customer care calls, and tried multiple setups and router settings.  Solution: Unbelievably, I think that the ultimate solution was the power cord itself.  I don’t know if the one given to me was the original, but reading one post somewhere from someone about getting the power cords mixed up after trying to get his 3GMC working again after a power outage was enlightening. He mentioned that a tech told him that the femtocells are very sensitive to the power supply!  The 3GMC sticker calls for a power supply of 12v, 0.8a. The manual says it needs 12v, 1.25a. My power cord was 12v, 0.5a! I found a power supply cord for a different device rated at 12v, 1a, so I tried it.  For good measure I logged into my account and disconnected the unit.  Then I re-registered it minutes later.  BOOM! In 30 minutes, I had a SOLID 3G light for the first time!  I think that it just wasn’t getting enough juice!  Overall, I tried many options and I had to learn many things.  I suggest taking a look at the power supply first and then these options to try to get your unit working: turn on auto DCHP setting on in your router, set MTU to auto in the router, IPSec pass-through enabled in your router, port forwarding in the router using the ports listed in the manual, disable Upnp setting in the router, check that Ethernet cables are through and not crossover type, power cycle 3GMC, router, modem multiple times, finally make sure the 3GMC can get a gps lock during activation by putting it by a window.  My equipment: Linksys CM100 cable modem-Linksys WRT54G2 router-3GMC.  Good Luck to us all, as I can only hope mine keeps working properly.