Q: Is it possible and safe to play and/or charge my iPhone 3GS on my Bose docking station that I use with my iPod?
A: It is perfectly safe to connect your iPhone 3GS to any Made-for-iPod Dock Connector accessory such as the Bose SoundDock. However, whether or not your iPhone 3GS will charge depends on the model of Bose docking station that you are using.
Last year, Apple dropped support for the older 12V FireWire charging standard from most of their iPods and the iPhone. This rendered a number of older accessories such as the original Bose SoundDock incompatible for charging purposes. Connecting the iPhone 3GS will display a warning notifying you that charging is not supported with this particular accessory.
Note that on these older speaker docks you can still listen to your iPhone through the speakers, but it will simply not charge from the Dock. In this case, you would either need to charge it separately with a different accessory or you will need to look at purchasing a third-party charging adapter such as the Scosche PassPort (iLounge rating: B) or Griffin Charge Converter (iLounge rating: B+).
Further, unless the accessory is specially made for the iPhone you will likely also receive a warning message warning you that you may receive interference from the cellular radio and prompting you to turn on Airplane Mode to avoid this.
Enabling Airplane Mode turns off the cellular radio on your iPhone, which will prevent interference with the speakers, but of course you will not be able to receive phone calls or data while listening to your iPhone. Note that this is only a recommendation, however; Airplane Mode is not required to use your speakers, and whether or not you hear any interference will depend on a number of factors, most notably whether you are using a 3G or EDGE connection; interference over GPRS or EDGE data connections is significantly more pronounced than over a 3G connection.