If you hear dial tone, but can't dial out. 
Please follow below to debug:

Case 1: After dialing, dial tone stop but won't make call:
    You need enter 10 digits (including area code) or press # to make call.

Case 2: After dialing, dial tone won't go away:
For some older model landline phone, it requires more power to operate.
Please Set "off hook power" to max
Please click here for instruction to change setting.  (set "off hook" power to max)