When you have a Busy status, Hubgets takes incoming calls and automatically transfers them to your voicemail. It doesn't hang up or drop your calls, so no worries.
The Notifications in the main menu will tell you who called while you were busy. If you click on the Call History button, you'll see the time details of your missed calls and/or if the person who called left you a voicemail message. Just to clear things, your caller will not experience any hangup or call drop.
One more thing, your calls will go straight to your Voicemail only if you've enabled the Voicemail active option. To do that, click on your profile picture next to the main menu, then press Communication devices. Slide to activate your Voicemail and set an answer time (in seconds) for it.