For any VOIP-based solution (FrontSpin or otherwise) you will want to use a hard-wired internet connection (plugging an ethernet cable directly into your computer) because VOIP traffic requires that voice data be sent and received simultaneously in order to have the clearest, most stable audio experience.
In technical terms, a hard-wired internet connection is full duplex, meaning that it can send and receive (or upload and download) data simultaneously. This makes the audio connection stable and provides the highest quality.
Wi-Fi is half duplex, meaning that the wireless access point (AP) can only send or receive data, just not at the same time. The AP sends a bit of data, then receives a bit of data, but cannot hold a stable, simultaneous connection for VOIP traffic. It is just a limitation of Wi-Fi technology.
VOIP will still of course work over a Wi-Fi connection, but it will potentially cause stutters or variabilities in the audio quality during calls, simply due to the nature of how Wi-Fi works. To avoid such issues, we (and all VOIP-based tools) recommend that you be hard-wired to the internet.