I would look into bundling your cable TV and internet from the same provider (Comcast, in your case). They usually have a pretty good bundle promotion rate. After 1 or 2 years, the price will go up. That's when you look at alternatives again.
As for cell phone, T-Mobile (and a few companies that re-sell T-Mobile service -- i.e. Mint, etc.) does indeed offer some compelling pricing. However, as a couple others posted above, when I tried them in my location, the coverage just wasn't up there for me. Dropped calls, calls not coming through, etc. I left them after 2 months.
I am currently using Verizon's Pre-Paid 5GB plan for one phone. It starts out at $40/month. But you get a $5 discount if you set up automatic payment from a credit card. So down to $35. Then after 3 month, it goes down $5 with a "Loyalty" promotion. Down to $30/month. That's where I'm at now. After 9 months, it drops another $5 with another Loyalty promotion. So $25/month. If you use more data than 5GB, they have other similar plans with more data. The key is use the "Pre-paid" plans.
Verizon coverage in my area is great. Never had one issue. I use less than 1GB of my 5GB allotment every month.