Hello @Bvlenci,
Maybe take a look at this thread:
I have been using Zoiper for years. In short, to receive calls without issues, you need to buy their service for push notifications. Otherwise you will never have reliable service.
I went with Groundwire which costs peanuts (and a one-time small fee) compared to a recurrent expensive monthly service with Zoiper.
You need push service and it comes with Groundwire.
For SMS, you must configure your account to forward SMS to the desired extension. Your application must support it. Groundwire does. It works.
Since I use an Android phone, I prefer to use the Voip.ms SMS app because it uses the API and I can have the full history of all SMS, whether I use the web interface, emails or any device. If you use Groudwire (or any other softphone), the SMS will be local to that device only. (Which makes sense as SMS are working like that.) But it works with Groundwire.
Yeah, you have to pay a little bit for Groundwire (only once) but frankly, it will not only save you a lot of headaches, but give you a very nice experience. I do not regret a single penny spent on Groundwire. And with Google Play, if you activate the “Family” play store thing, you can install it for free on other devices of family members. Which is nice! 
For instructions for Groundwire, SMS, push notification (and use call encryption, to make your life easier too) it is there:
https://wiki.voip.ms/article/Acrobits_Groundwire
(And SMS:)
https://wiki.voip.ms/article/Acrobits
Kind regards,
Alexandre