Everton,
They have an outdoor enclosure if you want. The real outdoor cams are a little expensive.
http://www.voipbaez.com/grandstream-gxv3662-wall-mountMy cam is on the inside behind some glass looking out onto the street. You definitely cannot use the indoor models outside unless it is out of reach because the plastic dome cover is easily removed. You can try to put together a DIY project to build yourself a glass or plastic enclosure. To get an idea on the wiring have a look here.:
http://www.grandstream.com/products/surveillance/gxv3611/documents/gxv3611_quickstartguide.pdfhttp://www.grandstream.com/products/surveillance/gxv3611/documents/gxv3611_usermanual_english.pdfThese are definitely professional grade cams. The cam has a built in mic and speaker. However there are connections to attach external mic and speakers as well. I have mine connected to a PBX. It is basically a sip end point. When someone rings the door bell (connected to an alarm input), you can have the camphone call you on your cell and you can buzz them in using the connected electric strike via DTMF tones. You can have a conversation with someone in front of the camera. For a complete description of equipment you can visit their website.
If you connect it to the OBi it will need to be connected like any other ip phone. I can imagine all sort of interesting things I could do with an OBi+this camera. It is actually described as an ip surveillance product. Surveillance software included.
If you only wanted video and audio to the door the price/value of the GXV3615W IP Cube camera- WIFI ($86) cannot be beat. This is less expensive than my webcam. Grandstream is one of the few selling sip enabled cameras. The quality is almost High Definition quality. You can call the cam via video softphone, video phone, or via browser. This is the best price I could find. The service was first rate as well.
http://www.voipbaez.com/grandstream-gxv3615w-ip-cube-camera-wifiIt's starting to sound like a sales pitch. Rest assured I'm not connected in any way to either Grandstream or Voip Baez. If you are into gadgets or are of need of a cheap wifi sip camera I would buy the $86 dollar model just for the novelty of it.
Since you mentioned that you already have the Doorfon and I assume that you own an OBi, I think you already have basically the same solution (minus the video feed). Connect the OBi to the Doorfon. You should then be able to open the door via DTMF. Of course you need to install the electric door strike.