Rest assured, your callers are able to leave voicemails. The message you are hearing is the Grasshopper call screening announcements you would generally hear when you pick up the call.
To stop this from happening, you should shorten the “ring for” time within your extension settings
To change this, sign in on the Grasshopper website, click Extensions, then select Edit on the Extension you want to change. Next, click Edit next to the forwarding number you want to update this setting on.
Select “ring for” and change to 25 seconds.
User Tip: Don't hit the 'ignore' button on your phone, as that will immediately send Grasshopper into your phone's voicemail. Rather than hit 'ignore' for calls, either answer the call and hit '2' to send the caller to Grasshopper voicemail, or answer the phone and immediately hang up.