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Do the wireless devices and the transmitter they are connecting with need to operate on the same frequency? For example, would my ipad need to operate at 900 mhz if the wi-fi router in my home is operating at 900 mhz? Is it sufficient for them to operate in a similar frequency range, say 875 - 925 mhz? If they are poles apart, say 300 mhz and 1200 mhz, will they be able to communicate with each other? I'm guessing whatever the answer to this question is, the same will apply to bluetooth devices pairing with each other.
First, to avoid confusion, standard Wi-Fi only operates at 2.4GHz and 5GHz, and not 900MHz.
Yes, the frequency of reception and transmission for most categories of device need to match up. This is because, for maximum efficiency, the communicating antennas must physically be of the same resonant wavelength, and the internal circuitry is factory preset accordingly.
Some devices are able to switch to make the best use of the available spectrum. But, being automatic, they still employ discrete frequencies and not ranges of same or wide band. One example is how a mobile phone will revert to 3G from 4G if the latter network is unavailable.
Of course, specialised equipment such as short wave or HAM transceivers ARE tunable over a continuous frequency range, but I assume that was not the subject of your question.
As an historical side note, crude spark gap transmitters were banned because they transmit simultaneously throughout a broad spectrum of frequencies thereby scrambling, or "jamming", licensed communication within discrete radio channels.
You are not alone. According to experts, over 35% of the world’s population feels some form of unwanted reaction to EMR exposure. Additionally, everyone is susceptible to induced biological abnormalities that may not manifest perceptibly for years or even decade.