Contact Apple with the information below. Apple officially says you can transfer it (to another person along with the phone or to another device within 30 days for the same owner).
The customer can also get a full refund if it's canceled before 30 days from the purchase date and a pro-rated refund, less cancellation fees, if it's canceled after 30 days from the purchase date.
From AppleCare Products FAQ:
Is the AppleCare Protection Plan or AppleCare+ transferable?
Yes. If you choose to sell or give away your Apple product, you can also transfer the ownership of the AppleCare Protection Plan or AppleCare+. Please see the Terms and Conditions for complete details.
For transfer, the terms and conditions PDF (for iPhone - USA) states:
10. Transfer of Plan
(i) With Transfer of Covered Equipment to New Owner. Subject to the restrictions set
forth below, you may make a one-time permanent transfer of all of your rights under the
Plan to another party, provided that: (a) the transfer includes the original Proof of
Purchase, the Plan's Confirmation and all of the Plan's packaging material, including
printed materials and these Terms and Conditions; (b) you notify Apple of the transfer
by sending, faxing or e-mailing notice of transfer to Apple Inc., ATTN: Agreement
Administration, MS: 217-AC, 2511 Laguna Blvd, Elk Grove, CA 95758, U.S., fax number 916
-405-3655 or firstname.lastname@example.org, respectively, and (c) the party receiving
the Plan accepts the Terms and Conditions of the Plan. When notifying Apple of the
transfer of the Plan, you must provide the Plan Agreement Number, the serial numbers
of the Covered Equipment being transferred, and the name, address, telephone number
and email address of the new owner.
(ii) With Transfer From Original Covered Equipment to New Covered Equipment. You may
make a one time, permanent transfer of the coverage under the Plan to a new Apple
product that is owned and purchased by you within thirty (30) days of the Covered
Equipment purchase. The new product must be eligible for coverage under the Plan and
at the time of transfer both products must be covered under the manufacturer’s
one (1) year limited warranty. Apple will issue a Plan Confirmation for the new product, which will then become the Covered Equipment. When notifying Apple of the transfer, you must provide the Plan Agreement Number, the serial numbers and Proof of Purchase of the products being transferred by sending or faxing, where available, notice of transfer to Apple as set forth in the section immediately above.
For cancellation and refunds, the terms and conditions PDF (for iPhone - USA) states:
You may cancel this Plan at any time for any reason. If you decide to cancel either call Apple at the telephone number below, or send or fax written notice with your Plan
Agreement Number to AppleCare Administration, P.O. Box 149125, Austin, TX 78714 -
9125, U.S. (fax number 916-405-3973). A copy of the Plan’s original proof of purchase
must accompany your notice. Unless local law provides otherwise, if you cancel within
thirty (30) days of your Plan’s purchase, or receipt of these Terms and Conditions,
whichever occurs later, you will receive a full refund less the value of any service
provided under the Plan. If you cancel more than thirty (30) days after your receipt of
this Plan, you will receive a pro rata refund of the original purchase price, based on the percentage of unexpired Coverage Period from the Plan’s date of purchase, less (a) a cancellation fee of twenty - five ($25) dollars or ten percent (10%) of the pro-rata
amount, whichever is less, and (b) the value of any service provided to you under the
Plan. Unless applicable local law provides otherwise, Apple may cancel this Plan for fraud or material misrepresentation. Unless applicable local law provides otherwise, Apple may also cancel this plan if service parts for the Covered Equipment become unavailable, upon thirty (30) days’ prior written notice. If Apple cancels this Plan
for the unavailability of service parts, you will receive a pro-rata refund for the Plan’s unexpired term.
Also see How to transfer coverage of an AppleCare agreement.