I've got it. The vehicle will be using Rogers for coverage. Have you tested Rogers coverage on a cell in your garage? Is it good, or sketchy? The install affects the coverage as things inside the vehicle can affect coverage, and every vehicle is different. But, if you have excellent Rogers coverage with a cell, I likely wouldn't worry.
You can also add a fob and antenna if you want. That way you could use the fob from inside the house (if the cell coverage isn't good enough) and leave the fob at home when you leave and just use your iPhone when you're out and about.
I've been in underground parking with mine and it didn't work, but I also didn't have any coverage on my cell in that location.
If anyone has any questions, feel free to ask.