Well after chatting with Trang from the AT&T wireless support department he recommended that I try re-registering the Microcell device at www.att.com/3GMicrocell which will apparently resolve the matter in his opinion. 

After going over some simple troubleshooting with Trang (check the cables, how many green lights etc) I was starting to give up hope and then my HTC suddenly reconnected to the Microcell out of the blue. I asked Trang if he had reset the device from his end and he said he was only "checking some settings" and said that if it happened again to just go reregister it using the tool on the website. 

While on the Microcell website checking the settings I noticed the device has a feature called "Automatic hand-out" which is currently enabled in my case. I asked Trang if he suspected it might help to disable this feature as I am not able to transfer calls from Microcell to ATT tower while leaving my house anyhow (there is no signal until the very end of my long driveway). Trang said that this would not resolve the "No service" issue we have been experiencing but if re-registering the microcell does not resolve the matter I am going to try that out anyhow...