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.
On Android, you have a couple of different options. If you don’t want to use Google Voice, you may want to check out the free version of any paid apps, as performance can vary from handset to handset.

An option with far fewer cables is the RecorderGear PR200. It records your conversation via Bluetooth. The call button in the middle of the device can answer calls on the Bluetooth-connected phone. Hold the PR200 up to your head to talk and listen, as if it's the phone. It also features a USB end to quickly access recordings on the computer. It will hold about 144 hours of conversation before it fills up the 4GB of storage. It also records like any digital recorder sans smartphone, since it has an external pin-hole microphone.
To set up your voicemail, press *98 from your home phone or call the retrieval number you received with your welcome letter. Voice prompts will guide you through the rest of the steps.