I've found that Walkie-talkies are unable to connect to a phone.
It will take some doing (or as they say now making) but it should be possible to do.
For example, have 4 walkie talkies one transmits on channel A another receives on channel A, the third one transmits on channel B and the last one receives on channel B.
Now you need something that allows voice detection and some buffering that allow time for the transmitter to engage, the receivers are always on.
The channel B receiver hooks into the phone microphone, the channel A transmitter hooks into the phone speaker, you also need some MCU with 2 ADCs and 2 DACs and buffers and logic that takes the phone off hook and can trigger the hang up. Dialing via DTMF (touch tone). The MCU also controls the channel A transmitter when voice is detected from the phone. For dialing. The MCU should also detect ringing and transmit it via some not normally used DTMF sequence that the remote system can interpret to ring the receiver.
On the remote system, you need a phone handset and wire the speaker via a ADC/Buffer/DAC controlled by an MCU that will detect voice to transmit on the channel B transmitter... well you get where this is going.
More complicated using only one pair of walkies. short transmissions and larger buffering and synchornization between receiving and transmitting periods, more complicated controls to use the tallkies as the transport. This might require to use some binary protocol (kind of like a modem) between the two stations.
Anyways, you can use walkie talkies but it's going to take some design and work. You can substitute the walkies with RF transmitters and receiver in the same fashion using two channels, but the problem will be what frequencies to use.