System is a MICS w/4.1 software (4 Port Flash w/2.0 s/w). An extension is forwarded to a cell phone and if you call the phone internally, it rings the cell phone. If the recept forwards an outside call to the extension, you hear the extension's voicemail (internal). The extension obviously has "Alow Redirect" on and the extension forwarding the call, has "Alow Redirect". The only thing I could think of was only one Intercom button on the phone, but I checked that and it has two. Any ideas.