The SIM900A is a compact quad-band GSM/GPRS module ideal for voice, SMS, and data transmission in embedded applications. Controlled via AT commands, it supports standard GSM protocols and is widely used in IoT, remote monitoring, and M2M communication systems.

Specifications

• Frequency Bands: 850/900/1800/1900 MHz
• GPRS Class: Multi-slot Class 10/8, Mobile Station Class B
• GSM Compliance: GSM Phase 2/2+
• Transmit Power:
  • Class 4 (2W @ 850/900 MHz)
  • Class 1 (1W @ 1800/1900 MHz)
• Control Interface: AT commands (GSM 07.07, 07.05, SIMCOM extensions)
• Power Supply: 3.3V – 4.5V
• Sleep Mode Current: ~1.0 mA
• Operating Temperature: -40°C to +85°C

Features

• Supports voice, SMS, and GPRS data transmission
• Integrated SIM card slot (flip type)
• SMA antenna interface for reliable signal reception
• Serial port with protection circuitry
• Compatible with SIM Application Toolkit
• Low power consumption for energy-efficient designs
• Mounting holes for easy integration

Some SIM900A modules require firmware reflash. If you are seeing the network indicator blinks fast continuously even after inserting a valid sim, then most probably the firmware need to be updated. If you are incapable of handling such a task with a USB to TTL module such as the FT232 module, then this module isn't suitable for you. In case the firmware needs to be updated, following tools could be helpful.

Serial Tool
Custom Flasher
Firmware