VoIP phone adapters (ATAs) bridge analog phone hardware with internet calling services, letting users cut traditional landline costs while keeping existing cordless phones and fax machines. The category serves home users with one or two phones plus small offices needing multi-line solutions. The wrong adapter fails to support fax or alarm panel signaling, locks the user to one VoIP service, or chokes on poor internet connections without quality-of-service controls. After comparing 10 current VoIP phone adapters across home, fax, and small office use, these seven balanced line count, codec support, SIP compatibility, and price.
Picks were narrowed by FXS port count, SIP protocol support, fax (T.38) capability, codec range, QoS features, security (TLS/SRTP), and provider compatibility lists.
Quick Comparison
| Adapter | FXS Ports | Codecs | Fax T.38 | SIP/Proprietary | Best for |
|---|---|---|---|---|---|
| Cisco SPA112 2-Port Adapter | 2 | G.711, G.729 | Yes | SIP | Overall |
| Grandstream HT801 ATA | 1 | G.711, G.722, OPUS | Yes | SIP | Budget single |
| Grandstream HT802 2-Port ATA | 2 | G.711, G.722, OPUS | Yes | SIP | Two line |
| Polycom OBi200 VoIP Adapter | 1 | G.711, G.722, iLBC | Yes | Google Voice, SIP | Google Voice |
| Polycom OBi202 Phone Adapter | 2 | G.711, G.722, iLBC | Yes | Google Voice, SIP | Dual Google Voice |
| Grandstream HT812 2-Port ATA | 2 | Wide range | Yes | SIP | Small business |
| Cisco SPA122 2-Port Router ATA | 2 | G.711, G.729 | Yes | SIP | Router built-in |
Cisco SPA112 2-Port Adapter, Best Overall
The Cisco SPA112 is the most widely supported SIP ATA across consumer and business VoIP services. Two FXS ports handle two separate phone lines or one line with extension. Cisco's mature firmware delivers reliable call quality with G.711 (full quality) and G.729 (low bandwidth) codecs.
T.38 fax protocol support handles fax machines reliably which most consumer ATAs cannot do. The web interface lets advanced users configure dialplans, codecs, and provider settings. Built-in QoS prioritizes voice traffic over data. SIP TLS and SRTP encryption support enterprise security requirements.
Trade-off: configuration interface assumes some VoIP knowledge. Beginners should use OBi200 with auto-provisioned services.
Grandstream HT801 ATA, Best Budget Single
The Grandstream HT801 is the lowest-cost ATA with full SIP support that works with every business VoIP provider plus DIY Asterisk PBX setups. Single FXS port handles one analog phone. Audio quality matches more expensive options through wide codec support including OPUS (high quality at low bandwidth).
Web interface configuration is straightforward for SIP provisioning. TLS and SRTP encryption protect call security. T.38 fax support included. Grandstream's firmware updates regularly with security patches and feature additions.
Trade-off: one phone port only. Users with multiple phones need HT802 or larger.
Grandstream HT802 2-Port ATA, Best Two Line
The Grandstream HT802 adds a second FXS port for households with two separate phone numbers or businesses with two lines. Each port can use a different SIP account from a different provider, which suits households mixing personal and business numbers on one device.
The HT802 supports the same wide codec list as HT801 including OPUS. T.38 fax support handles fax machines. The Ethernet port for WAN plus integrated firewall handles direct connection to home router without intermediate switch.
Trade-off: more configuration complexity than single-port ATAs. Two SIP accounts means double the provisioning work.
Polycom OBi200 VoIP Adapter, Best Google Voice
The Polycom OBi200 (formerly OBi200 by Obihai before Polycom acquisition) remains the easiest ATA for Google Voice integration. Auto-provisioning through the OBiTalk portal links the device to a Google Voice account in 5 minutes without configuration files or SIP knowledge.
The single FXS port handles one analog phone or cordless phone base station. Google Voice calling to US and Canada is free for personal accounts. The OBi also supports SIP for paired use with paid VoIP providers as backup or alternative.
Trade-off: Google Voice for personal accounts doesn't include 911. Pair with cellular backup for emergencies.
Polycom OBi202 Phone Adapter, Best Dual Google Voice
The Polycom OBi202 stacks two FXS ports on the Google Voice integration framework. Two separate Google Voice accounts can attach to the device, with each phone using its own number. Mixed setups (Google Voice on one line, SIP provider on the other) also work.
The 4 SIP service registrations support multiple providers simultaneously. Built-in router function allows direct connection to broadband modem without separate router for users with simple network needs.
Trade-off: aging hardware. Polycom has not refreshed the OBi line significantly in years. Newer SIP-first users should consider Grandstream HT802.
Grandstream HT812 2-Port ATA, Best Small Business
The Grandstream HT812 targets small business with two FXS ports plus enhanced security features. Three-party conference support, advanced call routing, and ringbank functions handle small office requirements. Per-port SIP accounts allow each phone its own number.
The HT812 supports HD voice through OPUS and G.722 codecs. SRTP and TLS encryption protect business communications. Gigabit Ethernet matches modern business network requirements. Firmware updates are signed and verified for security.
Trade-off: 2-port limit caps it at very small offices. Larger offices need IP phones or a PBX with multiple gateways.
Cisco SPA122 2-Port Router ATA, Best Router Built-In
The Cisco SPA122 combines the SPA112 functionality with built-in router and 2 LAN Ethernet ports. This suits users who want one device handling internet routing plus VoIP without a separate router. QoS rules prioritize voice traffic over downloads automatically.
The 2 FXS ports plus router function consolidates the home network into fewer devices. Cisco's enterprise firmware quality applies. Both T.38 fax and standard G.711 fax modes available for different fax machines.
Trade-off: integrated router lacks Wi-Fi. Users still need a wireless access point or separate router for wireless devices.
How To Choose
Match service compatibility to your provider
OBi for Google Voice. Grandstream and Cisco for business SIP providers. Check provider's supported ATA list before buying.
Port count matches phone count
Single phone: HT801 or OBi200. Two phones with separate numbers: HT802 or OBi202. Three plus phones: multiple ATAs or move to IP phones.
Fax requires T.38 support
Standard VoIP corrupts fax tones. Look for T.38 fax protocol support in both ATA and SIP provider for reliable fax over VoIP.
Security features matter for business
SRTP and TLS encryption protect call content from network eavesdropping. Business users should require both; home users can accept basic SIP.
For related reading, see our breakdowns of home VoIP services compared and cordless phones for VoIP. For how we evaluate networking gear, see our methodology.
VoIP adapters extend analog phone life through the internet calling transition. Match the adapter to the service you plan to use, verify fax support if needed, and budget for monthly service costs separately from the hardware.
Frequently asked questions
What is a VoIP phone adapter?+
A VoIP phone adapter (also called ATA - Analog Telephone Adapter) converts internet calling signals to analog phone signals so traditional handsets work with services like Google Voice, Skype, OBi, or business SIP providers. The device has an Ethernet port for internet connection and one or more RJ11 phone jacks for analog phones. ATAs let users keep their existing cordless phones, fax machines, and alarm panels while switching from POTS landlines to internet calling.
Does Google Voice still work with VoIP adapters in 2026?+
Yes, Google Voice continues to work with OBi200, OBi202, and certain Polycom and Grandstream adapters. Google sold OBi to Polycom in 2018 and the service has remained operational. Some older OBi models lost support; check current Google Voice ATA compatibility list before purchasing. Free Google Voice calling to US and Canada through OBi remains available with no monthly fee for personal accounts.
Can VoIP adapters work with fax machines and alarm systems?+
Sometimes. Fax over VoIP works best with T.38 fax protocol support in the adapter and at the SIP provider. Standard G.711 codecs cause fax failures because internet packet loss disrupts the modem tones. Alarm systems generally do not work reliably over VoIP because they need 100 percent uptime and clean tones that VoIP cannot guarantee. Most alarm companies require POTS or cellular backup, not VoIP.
What is the difference between SIP and proprietary VoIP services?+
SIP (Session Initiation Protocol) is the open industry standard used by business VoIP providers, Asterisk PBX systems, and most modern services. Proprietary services like Skype, MagicJack, and older OBi-to-Google integration use closed protocols. SIP adapters from Grandstream, Cisco, and Polycom work with any SIP-compatible provider, which avoids vendor lock-in. Pick SIP adapters for flexibility and proprietary adapters only for specific services.
Will my caller ID and 911 still work with a VoIP adapter?+
Caller ID works on most VoIP services for both inbound and outbound calls. 911 (enhanced 911 / E911) requires registering your physical address with the VoIP provider. Some providers (Google Voice for personal accounts) do not offer 911 service. Business and consumer VoIP providers (Vonage, Ooma, OBi with paid plans) include E911 but it depends on internet uptime which can fail during power outages. Maintain cellular backup for emergency calling.
Riley Cooper
Riley Cooper writes for The Tested Hub.