$540 via promo credit when you add a new smartphone line with your own 4G/5G smartphone on postpaid Unlimited Plus plan between 5/18/23 - 5/31/23 & port-in req'd. Promo credit applied over 36 months; promo credits end if eligibility requirements are no longer met.
DSL modems ultimately tie themselves into a single copper pair, so as pointed out above, the answer is no. If you want multiple DSL modems you'll need additional copper pairs connected and provisioned on Verizon's end. If you wish to use multiple modems on one line, only one modem may be active and powered up at a time. If another modem comes online, it will prevent both modems from receiving service.