Your iPhone can now send spam calls directly to voicemail — here's how to set it up. But, if your iPhone thinks it knows the number — like if you've called someone who isn't in your phone In one instance, for example, I had this turned on and my colleague's calls kept going right to my voicemail.
If you have voicemails saved on a non-smart phone, your best bet is to record them on a computer. This is a method that requires some equipment, but not as much as you might think.

When your phone only rings once then cuts out, this fault is known as "ring trip". It can be caused by a number of things either inside or outside your property, and will require a process of elimination to track down the cause of the fault.
If you don’t know what to say in your voicemail, here’s a few pointers to get you started: Make sure that you’re not yelling into the phone and the message is recorded in a somewhat quiet area. If the message is for work, try to keep it professional and avoid mistakes, if possible. If you’re working in retail, apologize for not picking up and note that you will call them back. Regardless of your occupation, try to keep the message short. It shouldn’t be longer than 25 seconds. If the voicemail is personal, feel free to leave a silly, short message that lets the caller know it’s you.