I currently have a Series 3 TiVo with two Comcast S-card cable cards in it. All has been working good & I was being charged $1.50 for each S-card. I recently switched cable TV packages. Basically went from an old promotion to a newer "double play" promotion. Well, I just got the bill and noticed they are now charging me 2 X $8.50 for my cable equipment. I had a similar situation happen in the past and had to jump through some hoops to get Comcast to get these S-cards back to $1.50 each. Had to explain how they were BOTH for one TiVo box. For this incident, I went to my local office and tried to get them to make the change again, but they were unable to and informed me I need to contact the Comcast billing department over the phone. I did so and the agent I talked to had to "escalate" the issue to a supervisor and they will get back to me. It got me to thinking and wondering if I could just use 2 M-cards in my Series 3 TiVo. I did some searching here and read the FAQ section. Found an area that stated this: You can use MCards in an original Series 3 box, but they will only function as SCards (e.g. you will need two MCards in an S3 to get dual tuner support Therefore, I guess I can. Its a long story why, but I'm also hoping that using M-cards will be easier for billing purposes (now & in the future). However, I remember when my Series3 first got installed, a Comcast technician had to do it and the guy who came only had one M-Card. He tried to get it to work in my S3, but couldn't. They came back the next day with the 2 S-cards and all worked good. I always thought M-cards wouldn't work based on this one experience, but does it require TWO M-cards to work in order to get ANY programming? Or can a Series3 run off one M-card and it was maybe just a fluke thing that mine didn't back then?