When I mentioned an electronic chip idea, what I had in mind is a
"microcontroller" with internal or external ROM, driving a speaker.
There are a number of such devices on the market, e.g., Motorola,
Parralax Stamp, Atmel, etc.  A Google search for microcontroller
should turn them up.

One version of the "Stamp" module has the outline of a 9-volt battery
but upon checking prices here in Australia it costs A$75, say US$30.
Other versions are both cheaper and more expensive.  However, the
programming unit for these microcontrollers seems to be around A$200
so unless you wanted to do a number of them, it would seem preferable
to find a company that can provide a programming service.

The chips used by Hallmark, etc., are about the size of a 5-cent coin
and are often called "blob" chips because the chip, which is quite
small, is encapsulated in a blob of black plastic goo.  You need to
order many thousands to get down to this level of miniaturisation.
On the other hand, the alternative suggestions of Ken Vinen and Pete
Woodworth in 020422 MMDigest are intriguing and could well solve the
problems more economically.

Keep in mind that a solid state device will usually be more reliable
in the long term.

Colin MacKinnon