Aircall is a bit different from GH. Our pricing is not final yet but if you're a lone user only receiving very few calls, GH will be cheaper.
If you're a team of a few people or if you receive or make a decent amount of calls/week, Aircall should be >20% cheaper at least.
if you're interested, drop me a mail at olivier@aircall.io so I can make you jump our waiting list (once you've tried the product I'll be happy to share with you our detailed pricing ideas - even if not final)