IP-PBX / GSM Gateway Specialist (Physical SIM Cards, USA)

Project Description:
We are looking for a specialist who can set up a virtual PBX system using physical SIM cards to handle SMS and voice calls in the USA (for bank verification, two-factor authentication, OTP delivery, etc.).

Important:
We need a reliable system for receiving SMS and calls from U.S. banks and online services via physical SIM cards, integrated with our infrastructure.
Virtual numbers from providers are not acceptable — integration must be done with physical SIM cards connected through GSM gateways.

Key Tasks:
• Assist with hardware selection and setup
• Build or configure an IP-PBX system (Asterisk, FreePBX, 3CX, FreeSWITCH, etc.)
• Integrate with GSM gateways (via SIP/IAX2)
• Connect physical SIM cards from U.S. operators (Verizon, AT&T, T-Mobile, US Cellular)
• Configure call and SMS routing
• Test bank SMS and voice call reception
• Optimize signal quality (antennas, frequency bands)
• Prepare brief technical documentationTechnical Requirements:
• Support for U.S. frequency bands: GSM 850/900/1800/1900 MHz, 3G/UMTS 850/1900 MHz, LTE (Bands B2, B4, B12)
• SIP trunk support
• Supported codecs: G.711, • G.722, G.729A, GSM
SIM hot-swap capability

Required Experience:
• Proven GSM gateway deployment cases
• Configuration of FreePBX, 3CX, or Asterisk
• PBX integration with web applications
• Understanding of U.S. carrier operations

Work Terms:
• Remote work
• Flexible schedule
• Project-based payment (to be discussed)When applying, please include:
• Experience with GSM gateways (models you’ve worked with)
• Examples of completed projects (if available)
• Estimated cost
Approximate delivery time