Message is a classic spell, one of the oldest and most useful out there. Here are some variations on it for when you want to play with magical telephony.
Black Fax
Duration: 3*[caster's level] minutes
Components: Your best imitation of a dial tone
Instead of conveying information this spell fills the target's head with darkness and static. Thought and movement is impossible for the duration of the spell while they receive the warped message. When it ends the target knows exactly who cast the spell. The target can't respond to anything happening around them, but can choose to make an INT or WIS save. On a success the spell only lasts half its normal duration, on a fail the duration doubles.
Spam
Components: A list of strangers' names and a shard of your soul
Sends an identical message to every intelligent creature within 1000'. They can't respond or tell who sent it. The spam message preempts or interrupts any other communication a target might receive. Spam can be cast as a cantrip to send 1 message, or with a spell slot to send [spell level] messages in sequence.
The message's subject is:
- Advertisements
- Unsound medical advice
- Sketchy pharmaceuticals
- Celebrity gossip
- Risky financial advice
- Thinly-veiled wire fraud
- Opinion poll
- Gambling
- Religious screed
- Vampire transformation testimonials
Party Wire
Components: 1 SP
Sends the same message to up to 10 targets the caster chooses. Each recipient can respond, but their return messages will get garbled if they try to reply at the same time and talk over each other. After the caster sends their message and hears all the responses roll even or odd. On even only the chosen targets got the message. Odd, the caster accidentally connected another person into the spell and they heard everything. GM decides who the extra person is.
Landline
Duration: Up to 10 minutes
Components: A little bit of your dignity
Lay face-down on the ground with your forehead pressed into bare soil. While in that position you can speak to 1 target and carry on a normal two-way conversation with them no matter where they are as long as their feet are touching the ground.