Verizon appears to be the only major wireless network operator in the United States that is not supporting the GSMA’s advanced messaging standard, dubbed Rich Communications Services (RCS).

Verizon representatives did not respond to repeated questions on the topic from FierceWireless. Meantime, T-Mobile, AT&T and Sprint have all reported progress to one degree or another on the rollout of RCS.

Sprint has been held up by the GSMA and Google as a primary driver of the RCS messaging standard in the United States. After Google threw its weight behind RCS in February 2016, when the GSMA announced the internet giant would create an RCS client for Android, Sprint in November of that year said it partnered with Google to launch RCS in the United States.

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And earlier this year, Sprint and Google announced the results of their efforts, noting that advertisers including 1-800 Contacts, 1-800-Flowers.com, Booking.com, SnapTravel and Subway, among others, have conducted advertising efforts using the messaging technology. Google, not surprisingly, has touted the advertising capabilities of RCS technology.

More recently, T-Mobile lifted the veil on its own RCS efforts. The carrier said it launched the technology in 2015 and that now every Android device the company sells includes RCS. Moreover, T-Mobile said that more than 30 million of its customers send over 250 million RCS messages every day.

T-Mobile noted that it’s working with Google to support RCS interconnection among operators, and that it is supporting the GSMA Universal Profile for RCS, which the carrier said is standard that will bring new features like larger file transfers up to 100 MB.

Finally, although AT&T has been largely silent on the topic, the carrier told FierceWireless that it launched RCS as “Advanced Messaging” in 2015 as a built-in capacity on the Messaging app available on the majority of its Samsung and LG smartphones.

“Customers with capable devices can send and receive RCS messages with other capable AT&T customers,” a carrier spokesperson noted. “Advanced Messaging provides indication of when a message has been delivered, read and when the other party is typing a response, plus the ability to share larger files such as full resolution pictures.”

AT&T also said it supports the GSMA’s efforts to develop the Universal Profile and the ability for features to work across wireless providers, though it didn’t provide any further details on those topics.

Those three U.S. carriers join a growing list of other international operators like America Movil, Freedom Mobile, Oi, Telia Company, Deutsche Telekom, Globe Telecom, Orange, Rogers Communications and Telenor Group in supporting Google’s RCS—Google said that carrier group represents more than 1.8 billion mobile subscribers worldwide.

RCS—initially dubbed joyn by the GSMA—is a messaging standard that was developed as a way for mobile operators to better compete with services such as WhatsApp, Facebook Messenger and Apple's iMessage, which have eaten into carriers' SMS revenues around the world. RCS supports features such as group chat and high-resolution photo sharing that aren't available through SMS.