Some jurisdictions will allow testimony/deposition by phone when a witness cannot be in the same location as the court. The person must be properly identified by a notary public.
In this case you aren’t actually putting your signature and seal on a document but you are verifying a person’s identity and in most cases placing the witness under oath. The witness information is recorded in the notary record book.
The biggest problem is that courts don’t always start when it’s time to do so and the notary may be waiting for long periods of time while things are happening in another location. This can be costly depending on how the person charges for their time. It can however be much less expensive than traveling to the other location.
Be sure to ask how you will be charged and how much time the person can allocate to waiting. The notary should provide a breakdown of fees charged. Separate fees for signatures from non-notary fees such as travel and time.
I always give people an estimate of the cost for travel, etc. before agreeing to the task.