You can use the test command to test the PSTN lines for dial tone and then dial a number, but you will not be able to talk or hear voice using this test.
The syntax for the test command is;
test o x (where x is the pstn line number). This will test to see if there is dialtone or not.
test d xxxxxxxx (where x is the digits to dial) will dial out the number you specify.
test e will end the testing.