latest version of mattermost shipped with gitlab is v2.2.0, while upstream mattermost is v3.0.3.
Since the mobile clients expect v3, there is no way to connect to gitlab-mattermost with a smart phone.
Is there a roadmap for bundling v3 with gitlab?
Also interested about update plans for new version of mattermost in gitlab omnibus package
Yes, Mattermost 3.0 not included in current Gitlab release.
They wrote on their blog, as to why:
Mattermost 3.0 is a major release requiring manual upgrade steps and therefore not included in 8.8 omnibus-gitlab package. Existing GitLab Mattermost users will have to wait until GitLab 8.9 where upgrade to Mattermost 3.1 should be automated. If you’re interested in reading more about how this decision was made, check out the issue on GitLab.com. Also the upgrade design for the next release will be discussed in the same issue so please share your feedback there: