A digital recorder is nice and all, but if you plug a recorder directly into an iPhone using a 3.5mm audio cable, you're not going to hear the call. Using the iPhone headphone jack—assuming your iPhone is so old that it even has one—cuts off the speaker. Get the Recap-C, a $99 adapter that plugs into an older iPhone's 3.5mm jack, with output to a headset as well as to a recorder. The secondary recorder—connected via a 3.5mm male-to-male auxiliary audio cable—is up to you. It could even be another iOS device (or Android or PC, but stick with the digital recorder for simplicity).
If you want to add another condition to your rule, select Add condition. You can add multiple conditions to a rule but do this judiciously so your rules don't become overly complex.

Here’s a simple clinician voicemail script if you want to keep your message to the point. Hello. You’ve reached Highland Family Counseling Services. We are currently unable to take your call, so please state your name, phone number, and a detailed message after the beep. We will return all calls within two business days.
You can delete individual voicemails as you listen to them, and most networks will automatically delete old voicemails after 30 days. However, few networks offer a simple way of deleting multiple voicemail messages when your mailbox is full – unless you can use an option such as Visual Voicemail, which lets you delete messages with a quick tap of your finger.