> Walkie talkies require a lot more power than smartphones have.

Yes and no. "Real" handhelds could broadcast at 5W but the Walkie Talkies that Radio Shack sold[1] were in the unlicensed band and limited to 10000 uV/m which is well within capabilities of a current cell phone power wise, as you note this would not be efficient with their antenna arrangement :-)

That said, it would be fairly trivial to use websockets to create a "PTT Walkie Talkie app" (think 2 person zoom meeting with no video)

[1] Exemplar Realistic TC-500 page 56 of this 1991 catalog: https://www.radioshackcatalogs.com/flipbook/1991_radioshack_...