If your cellphone service supports a data connection and you can figure out a way to connect it to the PVR, I don't see why you couldn't use that as well. But you'd have to make the calls manually instead of letting the unit update itself automatically.
You can use a broadband connection for the daily program update. With Tivo at least though, you have to use a phone line for the initial setup of the unit. But it doesn't have to be done at your house. You can bring it to a friend or family member's place and use their phone line.