I swithed from AT&T about 18 months ago and have been very pleased with Xfinity Mobile service and cost. The service has been better than AT&T in Northern California and since my wife and I are usually on Wi-Fi, our bill went from over $100 a month with AT&T to $15.00 a month with Xfinity Mobile. We are on the by the Gig plan and between us use less than 1 gigabyte a month.
I've been very happy since I switched from Virgin Mobile almost two years ago. My VM bills were a total of $37.50/mo. Most of my XM bills are less than $5.00/mo. If it's ever more than that it's still low, less than $20/mo, and only if I have to oay for 1 GB of data which might be three or four months in a year.
I've been on the by the gig plan, and keep my bills low by actively managing my mobile data usage. I do that by keeping mobile data turned off, and only turning it when when I need it.
Edit 6/30/19 12:39 PM - When I was with VM I paid for only one line. I'm paying for two lines with XM.
Too soon to tell, just switched 2 lines to Xfinity mobile, signal is better since they use verizon, a must here. looks much cheaper, but need a few months to confirm showing about 75.00 includine 1/24th of cost of 2 new samsung 10 e phones, that is far cheaper than verizon would have been.
I can honestly say that I have had nothing but positive experiences with my Xfinity Mobile service. I got the iPhone XS from them a year ago and I only got the "by the gig" $12 data service. I just added an iPad Air 3 to my Xfinity Mobile account and am loving that, too. I cannot complain about anything at all.