Strictly US regs...
14 CFR 91.21 Portable electronic devices.
(a) Except as provided in paragraph (b) of this section, no person
may operate, nor may any operator or pilot in command of an aircraft
allow the operation of, any portable electronic device on any of the
following U.S.-registered civil aircraft:
(1) Aircraft operated by a holder of an air carrier operating
certificate or an operating certificate; or
(2) Any other aircraft while it is operated under IFR.
(b) Paragraph (a) of this section does not apply to--
(1) Portable voice recorders;
(2) Hearing aids;
(3) Heart pacemakers;
(4) Electric shavers; or
(5) Any other portable electronic device that the operator of the
aircraft has determined will not cause interference with the navigation
or communication system of the aircraft on which it is to be used. [snip]
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Note the phrasing... There is no requirement that the operator shows that a PED causes interference before that PED is banned. Rather, a given PED is banned until the operator is satisfied that it will not cause interference.
So, if the operator doesn't want a pax using a GPS, it merely claims that it has not evaluated the GPS and the device is therefore banned. In the US I've seen some carriers allow GPS and some prohibit GPS use. Seems a little disingenuous though (one airline bans GPS regardless of aircraft type and configuration, while another allows GPS regardless of aircraft type and configuration. Doesn't seem like a decision based upon the actual potential for electronic interference really...) However, I do understand the argument that the jury is still out on this issue.
I'm completely supportive of a ban based upon security concerns and a rule change to support such a ban, if necessary. I just quibble with the current inconsistent rationale/explanation...
Dave