These surcharges on new phones — as distinct from activation fees charged to open a new line of service — aren’t new, but they are in the news after Verizon Wireless began imposing them and AT&T then increased its own fees.

At Verizon, the nation’s largest carrier, this $20 fee applies only to phones you buy from the carrier, either at full price or on its installment-plan program. A statement from the carrier explained that it “helps cover our increased support costs associated with customers switching their devices.” But if you bring your own device to the carrier, either purchased directly from a manufacturer or bought second-hand, the fee doesn’t apply. There’s also no such fee attached to phones bought for Verizon’s prepaid service .

Only two days after Verizon’s fee went into effect on April 4, AT&T increased its own device fee from $15 to $20. This, too, applies to phones bought at full price or on an installment plan from the carrier. The documentation of it at AT&T’s site suggests it also applies to phones you bring elsewhere, but AT&T PR clarified that the $20 fee cited there “is a one-time charge to activate a device on a new line of service.” So if you upgrade your current AT&T phone with one purchased elsewhere, you should not have to pay anything extra for the privilege of popping a SIM (Subscriber Identity Module) card into your new device.

Like Verizon, AT&T imposes no such fees on phones put on its prepaid service . Sprint, meanwhile, has not raised its device upgrade fee, but it was already at $30. That applies whether you lease the new phone from the carrier, buy it on Sprint’s installment-plan program, pay its full price or buy it a subsidy on its quietly-revived two-year contracts.