I have a 08 focus that had stock radio with the sirius button but when i pressed that button the display would say no sat radio.... so after alot of call and questions i was told that i had to have the reciever and to see if it was installed in trunk on drivers side behind the carpet in fenderwell..
i looked and nope didnt have it. I looked around for days for answers. heres what i did i went to ebay and bought another stock radio out of a 2010 focus got it installed and walla i now have siruis.
ford dealer said that 09 to 2011 came with the reciever built into the radio. so i looked at both radios side by side and sure enough there the same other than the 2010 has a esn # on it under the serial number and my stock 08 didnt.
anyways when i installed it i used my little sirius radio antenna that just sticks to roof by magenet but i did have to go to salvage yard and get just the end for the antenna plug i spliced it into my antenna and it works fine.
you can pick the radios up off ebay pretty cheap i gave $30.00 shipped for mine