I would think so, but AT&T would be who can answer the question. From:
https://www.att.com/wearables/#
Offer details
$55 CREDIT OFFER: Subject to change. Must purchase eligible device/have eligible devices and activate with eligible service. Eligible Devices: Requires (i) Apple Watch Series 3 purchase at full price, on installment agreement, or bring your own (excludes ones purchased on 2-year agreement) and (ii) HD-voice activated iPhone 6 or newer. Eligible Service: Both Apple Watch Series 3 and smartphone must be on same account with postpaid wireless voice & data services. (i) Apple Watch Series 3 requires min. $10/mo. when added to eligible shared plan;(ii) Smartphone requires min. $50/mo. for a new eligible plan (may be less if on an existing eligible plan). Bill Credit: Account and service on your line must remain active to get up to two credits ($30 service + $25 activation) w/in 3 bills. No activation credit if already waived. Offer Limits: Max. of 1 activation credit/waiver per device. One credit offer per eligible Apple Watch Series 3 activation. May not be combinable with other offers, discounts, or credits. Purchase limits as low as 2 apply. Other restrictions apply. Device Limits:
Apple Watch Series 3 requires AT&T NumberSync to access the AT&T cellular network. For SMS/MMS messaging, the synced iPhone must be on and connected to the AT&T network (via cellular or Wi-Fi connection; if using Wi-Fi connection, smartphone must have Wi-Fi calling activated). iMessage must be enabled on your iPhone. See
www.att.com/numbersync for details. Usage charges apply.