With the rapid evolution of mobile hardware and open-source telephony systems, the idea of using Android smartphones as GSM gateways has gained attention once again. In 2025, most Android devices ship with powerful chipsets (Octa-core and beyond), massive RAM, and enhanced connectivity options including 5G, WiFi 6, and Bluetooth LE. These advancements raise an interesting question: Can we now turn Android phones into full-fledged GSM VoIP gateways?

The vision is compelling—imagine an Android device running SIP or PBX software likeAsterisk or FreeSWITCH, connected via WiFi or cellular network, acting as a portable gateway for VoIP calls and SMS transmissions. Such a setup could drastically reduce deployment costs for call centers, remote offices, and developers in the telephony space.

However, despite the hardware readiness, several architectural and firmware-related challenges continue to block the realization of Android as a GSM gateway. Let’s break down where things stand in 2025.

The Current Use-Case: Android as a SIP VoIP Gateway

Today’s Android phones can reliably function as SIP VoIP clients. When configured with SIP credentials, these phones can:

• Register with cloud-based VoIP servers like Asterisk or FreePBX.
• Place and receive calls over the internet (WiFi/4G/5G).
• Utilize third-party SIP apps (like Linphone or Zoiper) for high-quality audio.

For outgoing VoIP calls, this is relatively straightforward. With some development effort, Android can also be used to route SIP traffic to other devices via hotspot tethering or local network setups.

But what about using the phone's actual GSM modem for making and receiving cellular calls programmatically—turning it into a GSM gateway?

The Real Challenge: Using Android as a GSM Gateway

Using Android as a GSM gateway essentially means controlling the phone’s cellular voice path—interacting directly with the modem, managing calls, and injecting or extracting audio data during active calls. This introduces three primary hurdles:

Hurdle 1: No High-Level Media Injection APIs

While Android offers robust media APIs for playback and recording, these do not extend to in-call audio paths. According to Google’s documentation:

“You can playback the audio data only to the standard output device. Currently, that is the mobile device speaker or a Bluetooth headset. You cannot play sound files in the conversation audio during a call.”

This limitation blocks developers from playing pre-recorded messages or injecting audio into a cellular call. Even in Android 14 and newer builds, this restriction remains due to security and privacy concerns.

Hurdle 2: Limited Access to Radio Interface Layer (RIL)

The Radio Interface Layer (RIL) is responsible for mediating communication between Android’s telephony stack and the hardware radio (modem). The control flow looks like this:

App Layer → Telephony Framework → RIL Daemon (rild) → Vendor RIL → Modem

Unfortunately, developers cannot interact with rild or the vendor RIL directly without rooting the device and modifying system partitions—an increasingly complex and risky task due to new Android security features like Verified Boot, AVB (Android Verified Boot), and SE-Linux.

Even if rooted, accessing rild functions doesn't guarantee media-level control over the GSM call.

Hurdle 3: Proprietary Vendor RIL Remains Closed Source

The final and most limiting factor is that Vendor RILs are proprietary. These are developed by hardware manufacturers (Qualcomm, MediaTek, Samsung, etc.) and are not open-sourced, even in custom ROM environments. Custom Android OS projects like LineageOS or GrapheneOS must still rely on these binaries, limiting the level of control available to developers.

This makes it virtually impossible to programmatically manage voice paths or GSM-level SMS without cooperation from the hardware vendor—something rare in the open-source community.

What’s Changed in 2025? Are There Any Workarounds?

Despite these limitations, some new developments and trends offer partial solutions or alternative routes:

1. Android SIP Integration + Cloud PBX

Most modern Android devices natively support SIP over WiFi or 5G. Using open-source PBX solutions like ICTCore, Asterisk, or FreeSWITCH, it's possible to configure Android phones as SIP endpoints or even lightweight gateways for outgoing calls via VoIP trunks.

2. Integration with External GSM Gateways

Rather than using Android phones, many developers now deploy affordable Raspberry Pi GSM gateways or open hardware (e.g., OpenBTS, YateBTS, GoIP, USB dongles with voice capability) that allow full call control, media injection, and GSM traffic routing.

These can be controlled via Android or web apps, achieving the same outcome without violating Android OS restrictions.

3. Use of Android as Control Interface (Not Gateway)

In enterprise setups, Android phones are increasingly used as remote control panels or user interfaces for telephony systems, managing call queues, viewing logs, sending SMS via APIs, and controlling actual gateways from a distance.

Why Proprietary Firmware is Still the Bottleneck

Projects like Replicant (a fully free Android distribution) have made attempts to replace proprietary RIL layers, but support remains limited to older devices with open modem documentation. Without vendor cooperation, accessing or modifying call flows within modern Android stacks remains unfeasible.

Conclusion: Android Still Can't Be a True GSM Gateway—But There Are Smarter Options

As of 2025, Android phones cannot be reliably used as GSM gateways due to fundamental architecture and licensing limitations. Although high-performance Android hardware and network speeds are suitable for SIP VoIP and unified communications, direct control over cellular modem functions remains blocked by closed-source vendor RILs and system-level restrictions.

What’s Possible:

• Use Android as a SIP VoIP endpoint.
• Remotely control external GSM gateways via Android.
• Use Android as a dashboard or control panel for PBX systems.

What’s Not Possible:

• Direct media injection during GSM calls.
• Complete programmatic control over GSM hardware.
• Building a full GSM gateway purely using Android hardware and OS.

Need Help Building an Open-Source VoIP or Telephony Solution?

ICT Innovations is a pioneer in open-source telephony consulting and development. Whether you need to build a custom VoIP gateway, deploy a multi-tenant PBX system, or integrate SMS/voice APIs into your apps, we provide end-to-end guidance.

Contact us today to turn your telephony ideas into reliable, scalable solutions.