If your incoming memory is full of old received or sent SMS messages, it is not possible to receive new ones. To receive new ones you have to delete old messages you no longer need.
The Gigaset 4010/15 Comfort/Micro can store a total of 13 SMS (depending on the country).
The devices Gigaset 4110/15 ISDN and 4170/75 ISDN can store a total of 25 up to 99 SMS (depending on the length of the SMS message).
The number of SMS to be stored may differ due to the capability of concatenated SMS with the Gigaset devices C100/C150, C200/C250 and S100/S150. The number of characters to be stored is about 4000.