Multitech MMCModem GPRS (MTMMC-G) Reference Manual page 12

Since the maximum length for the numbers in the ADN, FDN, and LND phonebooks is 60 digits:
•
if the user tries to dial a number that exceeds 60 digits: +CME: 3
Before the user can perform a call, the number of free records in the EF
store this number.
•
If there are free records left, the call is setup.
•
Otherwise, +CME: 20 error is returned (Memory Full).
See Recommendation 3GPP 11.11 for more details.
Multi-Tech Systems, Inc. Wireless GSM/GPRS AT Commands (Document Number S000293I)
Chapter 3 – General Behaviors
is checked for availability of free space to
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