I've done work with similar full duplex RF modules, and without the datasheet you're going to have a hard time working with them.
In order to implement multiple channels there's usually a PLL in there controlled by a microcontroller, which you would talk to via SPI. It takes a chunk of SPI data to set the radios up in the first place, and then you have to pair them which takes another smaller chunk of data to perform basic communications.
Further, they may or may not have data slicers in them, but even if they do you'll still end up needing to implement manchester encoding or another RF suitable data stream encoding in order to transmit data.
Lastly, they are very, very noisy. The phone and base station have a ton of filtering and compression in order to overcome the noise these modules typically have. This means your data stream has to be exceptionally robust.
However, if you are really committed to dealing them with no data sheet, you need to do one or both of the following:
Probe the lines with it connected and working in the handset and base station, and record all the digital setup data it uses. Also record when it pairs to see if you can understand how it handles that. Try to duplicate the setup, and dissect the pairing traffic so you can understand how to set the send and receive channel/frequency for each module.
Take the can apart and see if you can decode the circuit and read the chip part numbers. You may be able to get enough information from the circuit and chip data sheets to set it up yourself.
If you are merely interested in modules like that, but want to save yourself the frustrating and time, you should consider these:
They are easy to work with, though you still have to deal with the noise and data slicing issues.