Well biggest issue you will have with any speaker setup for the iPhone is that it is a
cell phone, and it uses GSM setup and that technology (as with any GSM phone) causes interference with speakers that are not shielded from it. So far there have been very few "Made for iPhone" speaker (or FM transmitters) systems. The one I pointed to is one of the few and smallest and cheapest systems that is "Made for iPhone" thus to get that certification from Apple, they have to shield properly. It does look small (though not as small as what you linked to) and does connect via the 3.5mm jack as requested, and for the price, isn't a bad setup. Looks quite portable too.
As mentioned, there are "computer" speaker phone setups uses for video conferencing some are USB, others use computer jack. Those with the jack could work with the phone and normally have long enough cable to get the speaker away from iPhone to avoid interference.
