Anatomy of a 64 SIM SMS gateway
Open the lid of the idea and a 64-port gateway is simple: 64 small GSM modem modules, each a complete radio with its own SIM holder, arranged in four rows of 16 across the top plate of a steel chassis. Every module has an SMA socket for its antenna and a power switch. Underneath, a backplane connects the modules to USB hub circuitry, and a mains power supply feeds the lot. On the unit we stock the rows are labelled 1-16, 17-32, 33-48 and 49-64, and the front panel carries the mains switch, IEC inlet and two pairs of USB ports.
How the host sees 64 channels
The chassis is organised as two banks of 32. Each bank's USB-B port connects to the computer, and the operating system enumerates 32 virtual serial ports per bank: 64 in total. Windows shows them as COM ports; Linux as /dev/ttyUSB devices. Nothing exotic is needed on the host; the same serial drivers that support a single USB GSM modem support the pool.
Your SMS software opens each port and speaks AT commands to the modem behind it. The important ones for a gateway are AT+CPIN? (SIM ready), AT+CREG? (network registration), AT+CSQ (signal), AT+CMGF=1 (text mode), AT+CMGS (send) and AT+CMGL/AT+CNMI (read or be notified of inbound messages). Multi-modem SMS servers handle all of this for you and present a queue, a log and usually an HTTP API to the rest of your systems.
Throughput, load balancing and channel independence
Each channel is an independent radio on its own SIM, so the 64 channels genuinely work in parallel. A single channel completes a standard 160-character message in roughly 6 to 10 seconds including network handshakes, which gives a practical planning figure of 20,000 to 35,000 messages per hour for a fully populated unit in good signal. Long, multi-part messages take proportionally longer.
Load balancing is the software's job: good SMS servers rotate outbound traffic across channels, respect per-SIM sending limits, retry on failure and route by prefix or SIM network if you ask them to. Because the channels are independent, one SIM being out of credit, out of coverage or removed does not stop the other 63.
Chaining two gateways
Next to each USB-B host port is a USB-A port. Connecting a second chassis to it lets both units share one host cable per bank, which is handy in a comms cabinet with limited ports. Two chained units present 128 serial ports to the host.
Power, cooling and physical handling
The gateway runs from 100 to 240 V AC through an IEC inlet and draws about 60 W with all channels active, so it does not need a special supply. Ventilation slots run along both sides of the chassis; leave a little clearance and it is happy on a shelf or desk. Two chrome handles on the top plate let one person lift and carry it. Specified operating temperature is -20 °C to +55 °C.
64-port SMS gateway in the UK
For UK use the modules register on 2G with EE, Vodafone or O2 SIMs (3G is switched off; Three has no 2G), and a 64-SIM gateway is a SIM farm under the Crime and Policing Act 2026, so we verify buyers before supply. Details: UK compatibility and lawful use.
Smaller gateways
If 64 channels is more than you need, the 8, 16 and 32-port models in the range are the same design in a smaller chassis. They are 2G units made to order with a 3 to 5 week lead time, and the 64-port is £591 less than the 32-port and £96 less than the 16-port, so most buyers take the 64 and leave slots empty. See the comparison.