In the process of setting up our Ooma Office system, at one point we set up a couple of extensions with call forwarding enabled with the forwarding number being a mobile number. These extensions were also placed in a ring group for all incoming calls. This worked fine until one of the users whose mobile phone was setup to have calls forwarded to it tried to call into our Ooma Office number. Because the user was on his mobile phone, when the forwarded call from Ooma Office rang on the mobile phone it immediately got the mobile number voicemail. It was impossible for these users to call into the office from their mobile phones.
To take the concept of "smart" call forwarding even a step further, it would be great if Ooma Office could recognize when ANY call that is forwarded is being sent immediately to voicemail and not forward the call in that situation.
Telo "forward all" or "multi-ring" would not ring the forwarded number if that number is calling. I suppose Ooma decided to do things differently with Office.
Also keep in mind, ring groups containing external extensions would count against your line capacity when that ring group is called. For example, if you have only 1 line, you can not have more than 1 external extension defined in your ring group or else the message "all phones lines in use, please try later" would be heard by the caller calling the ring group and the call would be terminated. While all line capacity taken, next caller would hear busy.
I didn't have time to test this until today. Setup my "Ring Group" to include my cell's extension and used the same cell phone to call the Office and the Office phones ring just fine and not forward back to the cell phone's voicemail. If this was a bug, Ooma must have fixed it.