@bcsteeve Well then I can tell you for sure, given the experience of myself, my daughter and my sister, that the way to go is 100% cellular with some sort of backup (in my case that's fongo.com on my iPod and speakout7eleven on an old flip phone).
To be sure of the promo activate a plan now, then wander about next week looking at phones/features and take the plunge!
Plus; it's 100% expense, no capitalization required. Fingers crossed it doesn't create a loss carry forward! 
If you're looking at the fact the phones are subsidized as part of the $140 per month your friend is paying, you have to remember the purchase price of the phone is spread over 24 months. And remember, the price of the phone is cheaper for the carriers then it would be to the general public. That $900 Pixel XL might cost the carrier $600. At that price it's costing you $25 to pay for the phone (if not more). Some people in here have broke down the costs, and in the long run, the carrier makes about $100 to provide the phone to you.
With Public Mobile, you need to bring your own phone, so basically you're paying for the bare bones services. You pay for what you need, and nothing more. I believe the term "no frills" is what's used to describe a carrier like PM. When you buy an unlocked phone outright, sure it'll cost you a lot more, but it doesn't mean you need to start with an iPhone 7 that's $1050 outright. @Jsauter mentioned an Xiaomi phone for $200. I've seen the newest Blackberry offerred on Amazon for $400. Just remember to separate the "phone purchase" from the "phone service" when trying to figure out if something is worth it.
$40 per month (and actually $38 per month if you enable autopay with your credit card) is a pretty good price for 4GB of data... but remember, it's province-wide calling. That may not affect you if you don't travel out of your province. The other thing to consider... when PM gets overwhelmed like they have with this promotion, unfortunately customer service won't readily be available. If you have no issues, then you can bypass all of that, but when you do need help, just realize customer service is provided through this community forum by one of the moderators or by email. You'll need to be a patient man!
I am like you that I work from home, and I find I only use maybe 300MB of data in a month. In my case, I'm thinking I'll skip the promo and stay with the 1GB per month plan (spread over 90 days), which ends up costing $35 per month with autopay ($105 each 90 days). Taxes will be charged on your first renewal (not on the initial payment).
My suggestion to you... if you don't need all the data, save yourself even more money... don't go with the promo, but instead the 1GB data plan. If you're okay with province-wide calling, skip the Canada-wide (saves you $5 per month).
...and hey, if you decide to get a phone... there will only be 2 guys left in Canada without a phone!! 
