Strategies against jamming attacks?

Jamming is the radio equivalent of shouting. The jammer drowns your communications under a lot of noise. Defence against jamming usually is a combination of the following:

• Power: speak louder. I.e. increase the power of your radio-emitting apparatus, so that it will take more noise to drown it. Of course, this increases energy consumption and heat dissipation, and it is not necessarily workable with your devices at hand.

• Tightening: try to use directional radio beams. The sender will send a non-isotropic signal, much stronger in one direction than in any other; the receiver will also concentrate its reception ability on this specific direction. This has been used in aircraft navigation systems (see this). This kind of solution requires directional antennas, and, more importantly, proper orientation: the sending device must know the approximate direction of the receiving station, and vice versa.

• Frequency hopping: switch frequencies over a large range of possible frequencies. Sender and receiver agree upon the sequence of frequencies that they will use. This relies on the idea that it is much harder to jam a large spectrum than a single well-defined frequency. GSM/3G signals already includes frequency hopping, and the sequence is nominally unpredictable by outsiders because it is agreed upon under the cover of the cryptographic layer (subject to possible weaknesses of the cryptography as used in GSM, of course). Note, though, that in normal marketable equipment, frequency ranges are legally constrained, and it is still relatively easy to jam all frequencies which have been allocated to GSM and 3G.

• Retaliation: a jammer is an active attacker; it emits a strong signal. This allows for tracking the jammer, and send armed goons to shut it down and appropriately reward the jammer operators, e.g. with some free dentistry.

The bottom-line is that if there was a way to force communications to go through even in the presence of active jammers, then the Military would use it. But in the battle between jammers and defenders, the jammers are currently winning.

Jamming is used either by fools or by clever professionals.

• The jammer can be triangulated by professional-level direction-finders (see source of this answer for a sample link) in half no time (unless special steps are taken by the attacker)
• What is jammed cannot be eavesdropped (okay, it's not as easy as that, but will suffice for the simplest case)
• Jamming forces the jammed parties to switch to Plan B which may be less prone to interception/interference

Why do clever professionals use jamming?

• To gain tempo in a fast-paced situation (like a physical attack)
• To deny the adversary the opportunity to communicate time-critical information

What do you do if confronted (or possibly confronted) with RF kiddies?

• Jamming outside of law enforcement and the military is highly illegal. Contact the relevant government authorities. In advanced countries radio spectrum is being monitored almost continuously and almost in all high-value locations. While you won't be able to get in touch with those who do the monitoring and provide quick response easily, your communications regulators will be able to do that (subject to vagaries of bureaucratic nature).
• Be prepared to switch to another mode of communication/radio band: VSATs, sat phones, troposcatter, Ham Radio modems, landlines.

What if you are against smart professionals?

• Plan your communications and responses long before you have to act.
• Chances are you are way behind the reaction curve when professionals resort to jamming.
• Do not rely on communications. Rehearse standard operating procedures and drills. Make sure you can guess what your buddy does next without going on air.

If you still want to design jamming-resistant protocols, please consider winning a government/military contract, hiring a bunch of smart professionals, learning plenty of stuff about electronic warfare etc. etc.

Active jamming is highly illegal, and if you report it the FCC should respond rapidly. Of course, that depends on your usage model (and your threat model). The problem is that you'd have to determine if it was being deliberately jammed, and not simply interfered with. The nature of the unlicensed bands is that even legal devices can simply have faults that cause them to broadcast noise. As a user of a Part 15 device, it's up to you to solve the problem first, if you can.

If you are concerned about someone jamming a stationary installation, a jammer would not be able to stick around for long without risking being caught. If you are concerned about a mobile application (jamming GPS signals in a vehicle, for example) you'll be moving and likely won't be in the area of jamming for very long. If you are, then the jammer is in your vehicle, and you've got some other problems.

Others have mentioned frequency hopping as a mitigation. Bluetooth (one of the protocols you specifically mentioned you're considering) uses an adaptive frequency hopping scheme that jumps around 79 different frequencies, and adapts to avoid congested frequencies, making it robust at rejecting accidental narrowband interference.

Otherwise, I'd advise you to treat RF communications as you would any network connection, subject to outages and interruptions. That might mean queuing up undelivered messages, standing up default behaviors when the networks are unavailable, switching networks to avoid problems, adding redundant network paths, sending alerts for a network link failure over a certain duration, etc. If you plan for it to be occasionally interrupted, you'll always be in a position to recover.