Sony SPP-A250 Operating Instructions Manual page 20

=>Making and receiving calls
bmlalcsicicsaleacmelaai a:
0 | Using as a telephone
The cordless handset can work on ten channels, so if you
experience interference while using one channel, you can
switch to another channel to improve the sound quality of
your cordless phone conversation.
@ interference while dialing
If interference noise occurs during dialing, you hear
five short error beeps. When this occurs, move closer to
the base unit.
@ Interference during a conversation
Press CHANNEL.
The phone will select a new channel. You may hear
noise for a moment. When the noise stops, continue
your conversation. If interference continues, move
closer to the base unit.