First, most of his problems are probably because he's roaming, not because of the phone itself. If he's happy with the phone, the phone is functional, and the phone is carrier unlocked, and is potentially compatible with either AT&T or T-Mobile (probably only T-Mo, truthfully,
AT&T may or may not), that's always a potential option.... but I'd need to know what the exact model of Alcatel Flip being used to find that out, and you'd need to make sure that it was carrier unlocked by the current carrier up in Canada first.
4G LTE is really all he needs and the lowest end network in the States now, and all you'll be able to get network wise on modern feature phones.
No matter what network works best in your area, I'd highly recommend looking into
US Mobile as well as Ting, since their plans can be gotten on all three major networks (DarkStar=AT&T, Warp=Verizon, LightSpeed=T-Mo), and they have an "unlimited" light plan for $10/month or $96/year with a $3/month or $36/year international calling add-on that provides unlimited calling to Canada, and that includes all taxes and fees. They also include free international roaming with some of their plans, and offer an optional $15/month international roaming add-on that provides 150 minutes, 150SMS, and 1GB of data that'll largely go unused under the circumstances. May or may not work out cheaper than Ting, but it's definitely an option if AT&T winds up being your best coverage network in the area. But still, run the numbers with his usage history. US Mobile might work out to be cheaper than Ting depending on the plan and roaming minutes.
If the phone needs to be replaced, however? There's not a lot of unlocked, big button feature phones with 4G LTE support anymore. There are vendor lock-in MVNO options like
Lively's Jitterbug Flip 2 (which I don't believe Lively's calling plans have international calling options), or more mainstream feature phones with smaller buttons that aren't so elderly friendly (a good way to find a good assortment of these sorts of feature phones would be searching for "
kosher phones" which, if nothing else can help you find specific model numbers of phones if you don't want it locked down on data and features) but of the unlocked independent type with big buttons? Due to the LTE switch and network vendor lock-in, the generics really can't use anything but T-Mobile as the network anymore. Of those options, Easyfone has the widest selection with the following three models, but you'll need to use a T-Mobile based MVNO which may or may not work in your area as well as other networks:
Easyfone Prime A1Easyfone Prime A6Easyfone T6Otherwise, there's the
Nokia 2780 Flip, which should work on either T-Mobile or Verizon's network (Verizon being the safest network suggestion bet not knowing where you are), and US Mobile has it available in their store for $90, which is the same price as HMD has it for sale directly.
Otherwise, if you cave and give up and go smartphone anyway, be aware of
Grand Launcher and
BIG Launcher as ways of making a smartphone more elderly friendly. Unfortunately, the open source Baldphone I used to recommend is now a dead project.
Hope this helps!