Acer Liquid Z500 - SIM Selection for Calls and Messages

Managing your SIM cards - 63
Selecting which SIM to use when making a call
If you have set Voice call to Always ask, you will be asked which SIM
to use each time you make call. Enter the number, then tap . A
dialog opens; tap the SIM to use and the call will be connected.
Selecting which SIM to use when sending a text message
If you have set Messaging to Always ask, you will be asked which
SIM to use each time you send a text message. Enter the message
and recipient information, then tap Send. A dialog opens; tap the SIM
to use and the message will be sent.