With Yeastar S-Series, all the telephony interfaces are modular and customizable, whether it’s FXS, FXO, ISDN BRI, GSM/3G, or E1/T1/PRI. S20 has 2 onboard module slots, S50 and S412 supports 4. S100 and S300 require the combination of Expansion Board and Telephony Module to add telephony interfaces. S100 allows 2 Expansion Boards and S300 supports 3.

• 1 Channel for GSM Voice Calls Frequency: 850/900/1800/1900 MHz (quad-band)