The free version displays a banner ad. In 2024, the ad servers for Zoiper 3.5 may be defunct or redirected to malicious domains. Either upgrade to Pro (if you have a key) or switch to the free version of Zoiper 5, which uses safe, internal ads.
If you have a valid Zoiper 3.5 Pro license, by all means, continue to use it—it remains one of the most reliable softphones ever written. But if you are a new user looking for a place to start, download the latest free version from the official Zoiper website. The nostalgia of 3.5 is not worth the security headache. zoiper 3.5
Zoiper 3.5 was last patched around 2016. It does not support modern TLS 1.3 encryption. Your SIP password could be sniffed on a public Wi-Fi network. Never use 3.5 over public internet without a VPN. The free version displays a banner ad