I already figured this out on my own through reading the FCC rules for FRS, and a few postings on other boards about kids' repeaters being shut down.
§ 95.194
(FRS Rule 4) FRS units.
(a) You may only use an FCC
certified FRS unit. (You can identify
an FCC certified FRS unit by the label
placed on it by the manufacturer.)
(b) You must not make, or have
made, any internal modification to an
FRS unit. Any internal modification
cancels the FCC certification and
voids your authority to operate the
unit in the FRS.
(c) You may not attach any antenna,
power amplifier, or other apparatus
to an FRS unit that has not been FCC
certified as part of that FRS unit.
There are no exceptions to this rule
and attaching any such apparatus to
a FRS unit cancels the FCC
certification and voids everyone's
authority to operate the unit in the
FRS.
(d) FRS units are prohibited from
transmitting data in store-and-
forward packet operation mode.
[61 FR 28768, June 6, 1996, as
amended at 68 FR 9901, Mar. 3,
2003]
Although part d only applies to data, part c is very clear and sort of terse. I even wondered about headsets that weren't tested with the unit until I read that speaker mics fall under a sort of blanket coverage. Basically, anything that can extend range is forbidden. They almost want the units physicaly in your hand or attached to your body. This calls into question Bluetooth enabled adapters such as for motorcycle communications. Unless it is one of the newer units with Bluetooth built in, what you attach may void your licence by rule. I wondered why there were so many European PMR adapters, and a relative few here mostly dedicated to bussiness radios.