You have several things to consider here:

1) Making sure the phone matches the bands offered by his mobile provider in his area. For example, T-Mobile has greatly expanded their band 12 coverage over the past year, but most mobile phones don't have band 12 coverage.

2) The actual RF qualities of the radios on the mobile phones.

3) Many mobile providers offer Wi-Fi calling, so this can be an alternative in a poorly covered area. However Wi-Fi calling is dependent on device support.

4) Many mobile providers offer free or cheap repeaters that connect into your cable modem or DSL routers. These emulate LTE or 3G base stations and can be used to make calls in poorly covered areas. This too works well in homes, and with any devices.

Thanks on pt 1 and 2. He's actually a pre-paid tmo customer. Unfortunately the wifi and repeaters seem only for post-paid customers

Could he move to post-paid? WiFi calling is amazing in areas with bad reception. In the basement at my work, WiFi is the only way to go.

He spends at most $50 a year on pre-paid so economically does not make sense.

Republic wireless (on the Sprint network) would be a relatively low cost option to try another provider and add WiFi calling. Their fee is $10/month plus data. That would be more than the $50 you pay now, but still manageable.

My experience, as an end user in the US, is that reception correlates more strongly with carrier than with phone model. Comparing carriers at your father's matters more than online reviews, I suspect.

I'd suggest you head on over to:

http://opensignal.com/coverage-maps/US/

And look at signal strength from the major networks. Most smartphones use "off the shelf" cell radios with "off the shelf" antennas. Phone shell materials make a little difference (metal Vs. plastic/glass) in particular if they're poorly grounded[0][1]. But overall I'd say look at network coverage first and foremost, and then look into if you can get a femtocell from the carrier to install in your house.

[0] http://www.wired.com/2010/06/iphone-4-loses-reception-when-a... [1] http://www.pcworld.com/article/202371/smartphone_antenna_tes...

Rather than focus on the phone, could you look into getting a femto cell installed?

In my country some of our providers support these and you can buy/install them legally. You could contact your networks to see if they support this.

https://en.wikipedia.org/wiki/Femtocell

I had an old Nokia candy bar that used to get great reception. If he's just making calls this could be good, plus in a low reception environment batteries drain quickly too so the candybar would be suitable.

Grossly simplifying and considering brands with all else being equal, Motorola has historically had great RF engineering, Nokia is good, LG and HTC would be good to average, and Samsung and Apple would be average to mediocre. This is truly a gross simplification, as all else is not equal: it depends on the specific model of phone (sometimes differing greatly between carrier), the bands used in an area, etc.

Ultimately, the only sure option is a "live fire exercise". Apart from that, maybe try a reddit subforum for where your father lives and see if they have good, local advice?

Ask some of your fathers neighbors what phones they use and how their reception is.

That's a good idea, though I think I'll probably get a lot of grumbling. I know one person who has both an iphone and a samsung (and previously a crackberry) that has had the same issues with both tmo and att. His experience is slightly better in that he gets some reception but suffers a good amount of drops.

Prior to using the Samsung Focus my father had a moto feature phone and generally was able to make calls over tmo.