There is a good chance I will be dead in 10 yrs time-- I hope not providing I can still wipe my own bum.
I do have a Nokia 6630 on Orange - I also thought it would be cool to have a smart phone - spent 4 days trying to get it to work when I found out the 4 bar signal wasn't to say I had a signal it is just there and light's up when you have a signal- my Nokia only shows a signal if one is there - I was confused - so needless to say it is useless here at home - This is on Giffgaf - I resent paying for two lines and have to think of wife who is smart phone dumb.
There's no standard way of displaying a phone signal strength, so one bar on your Nokia might be two bars on a Motorola or four bars on a new Samsung. Obviously some phones will have better antennas etc but just judging based on the bar value isn't that useful.
Most of the networks (Orange, O2 - not GiffGaff annoyingly which I'm on) support wifi calling I believe where if you have poor signal it'll make/receive calls over your wifi instead of the phone network. Or you can get booster boxes like EVH mentioned.