That depends on how many simultaneous calls you want to receive, but in general, your average home-level connection will work.
You just need to make sure the latency is as low as possible. Having a really fast broadband speed does not guarantee to have a stable and reliable connection.
Having high speeds works for streaming services like Youtube or Netflix and to download files. But when it comes to voice calls, this requires a stable connection because of the real time transactional of calls.
Also if you're wireless connected to the internet (like the WiFi on your home) you should check if there is no issues on the radio of the internet box or router.