One of my customers has been weighing the options of using Lync Online vs Lync On-Premise. There are a lot of questions about the feature sets available between the two offerings. The Microsoft Office 365 community has posted this chart for review.
http://community.office365.com/en-us/w/lync/480.aspx
The following matrix compares features across the delivery models for Lync Server 2010 (on-premises), Lync Online, and Office Communications Online (“OC Online”).
| Feature | Lync Server 2010 | Lync Online | OC Online |
| IM and Presence | |||
| 1-to-1 and multiparty IM/presence | Yes | Yes | Yes |
| Address book search | Yes | Yes | Yes |
| Distribution list (DL) expansion (DLX) | Yes | Yes | Yes |
| File transfers | Yes | Yes | Yes (inside firewall only) |
| PC-to-PC audio/video (A/V) dial-out calling | Yes | Yes | Yes (inside firewall only) |
| Click-to-communicate from Office applications | Yes | Yes | Yes |
| Interactive contact card in Office 2010 | Yes | Yes | No |
| Lync skill search in on-premises SharePoint Server | Yes | No | No |
| Lync skill search in SharePoint Online | No | No | No |
| Persistent Group Chat | Yes | No | No |
| Privacy mode | Yes | Yes | No |
| Lync External Connectivity (Federation and Public IM Connectivity) | |||
| IM/Presence and A/V Federation with other organizations running Lync Server, Lync Online, or Office Communications Server | Yes | Yes | No |
| IM/presence and A/V federation with Windows Live Messenger | Yes | Yes | No |
| IBM Sametime federation | Yes | No | No |
| IM/presence federation with Extensible Messaging and Presence Protocol (XMPP) networks (including Jabber and Google Talk) | Yes | No | No |
| IM/presence with AOL and Yahoo | Yes | No | No |
| Meetings (A/V and Web Conferencing) | |||
| Meeting attendee capacity | 250 | 250 | No |
| Desktop sharing | Yes | Yes | No |
| Application sharing | Yes | Yes | No |
| White boarding and annotations | Yes | Yes | No |
| PowerPoint upload for online presentations | Yes | Yes | No |
| Upload for other Office file types | No | No | No |
| Polling | Yes | Yes | No |
| Multiparty PC-based A/V | Yes | Yes | No |
| Unauthenticated experience in Lync Web App | Yes | Yes | No |
| Unauthenticated attendee (rich client) | Yes | Yes | No |
| Authenticated experience in Lync Web App | Yes | No | No |
| Scheduled conferences (using the Online Meeting Add-in for Lync 2010 in Outlook) | Yes | Yes | No |
| Outlook delegation for scheduling regular meetings | Yes | Yes | No |
| Outlook delegation for scheduling online meetings | Yes | No | No |
| Support for RoundTable conferencing device | Yes | Yes | No |
| Lobby | Yes | Yes | No |
| Interoperation with certified partners for dial-in audio conferencing | No | Yes | No |
| Provisioning for dial-in audio conferencing service for Office 365 direct customers | No | Yes | No |
| Phone dial-out from scheduled meetings via third-party dial-in conferencing service | No | Yes | No |
| Client-side recording and playback | Yes | Yes | No |
| Server-side recording and playback | No | No | No |
| Generate a link to a scheduled meeting via web page | No | No | No |
| Schedule an online meeting in Outlook Web App | No | No | No |
| Schedule an online meeting in Lync Web Scheduler | No | Yes | No |
| Dial-in audio conferencing on Lync Server | Yes | No | No |
| Multimedia content upload | No | No | No |
| Screen shot capture (including annotation) | No | No | No |
| Backstage/content preview for presenters | Yes | Yes | No |
| Mute all attendees | Yes | Yes | No |
| Mute individual attendees | Yes | Yes | No |
| Unmute all attendees | Yes | Yes | No |
| Unmute individual attendees | Yes | Yes | No |
| In-meeting attendee permission controls | Yes | Yes | No |
| Interoperability with on-premises video conferencing systems | Yes | No | No |
| Voice and Telephony | |||
| PSTN calling (incoming/outgoing calls) | Yes | No | No |
| Call hold/retrieve | Yes | No | No |
| PSTN dial-out for meetings | Yes | No | No |
| Advanced call controls (including transfer, forward, and simultaneous ring) | Yes | No | No |
| Access to Exchange Online voice mail | Yes | No | No |
| Team calling | Yes | No | No |
| Delegation for voice (for example, boss delegates to admin) | Yes | No | No |
| Call park | Yes | No | No |
| Outgoing Direct Inward Dialing (DID) manipulation | Yes | No | No |
| Enhanced 9-1-1 (E9-1-1) | Yes | No | No |
| Dial plans and policies | Yes | No | No |
| IP desk phone support | Yes | No | No |
| Survivable Branch Appliances for branch office resiliency | Yes | No | No |
| Call admissions control (CAC) | Yes | No | No |
| Support for analog devices (for example, fax) | Yes | No | No |
| Response groups | Yes | No | No |
| Private line (secondary DID for executives) | Yes | No | No |
| Interoperation with third-party private branch exchange (PBX) | Yes | No | No |
| Presence interoperation with third-party PBX | No | No | No |
| Remote call control (RCC) (also known as “click-to-call”) with on-premises PBX | Yes | No | No |
| Malicious call trace | Yes | No | No |
| Unassigned number | Yes | No | No |
| Network Quality of Service (QoS) – Differentiated Services Code Point (DSCP) | Yes | No | No |
| Media path optimization | Yes | No | No |
| Phone number management | Yes | No | No |
| Call detail recording (CDR) and billing reporting | Yes | No | No |
| Integration with call center solutions (Aspect) | Yes | No | No |
| Client Support | |||
| Lync 2010 | Yes | Yes | No |
| Lync Web App (for participating in scheduled meetings) | Yes | Yes | No |
| Lync 2010 Phone Edition (IP phones for Lync) | Yes | No | No |
| Lync 2010 Attendee client (for joining meetings) | Yes | Yes | No |
| Lync 2010 Attendant client (receptionist rich client) | Yes | No | No |
| Lync for mobile devices | Yes | Yes | No |
| Office Communicator for Mac | Yes | No | No |
| Office Communicator Web Access (2007 R2) | Yes | No | No |
| Office Communicator 2007 R2 | Yes | No | Yes |
| Office Communicator Mobile (for Windows Mobile 6.x phones) | Yes | No | No |
| IM and media encryption | Yes | Yes | Yes |
| IM filtering | Yes | Yes | Yes |
| Anti-malware scanning for meeting content and file transfers | Yes (partner solutions) | No | No |
| IM archiving (server-side only) | Yes | No | No |
| Exchange and SharePoint interoperability | |||
| Presence interoperation with Exchange and SharePoint on-premises | Yes | Yes | Yes |
| Presence interoperation with Exchange and SharePoint Online | Yes | Yes | Yes |
| Exchange Unified Messaging (UM) interoperation with Exchange Online | Yes | No | No |
| Exchange UM interoperation with Exchange on-premises | Yes | No | No |
| Hybrid Lync Online and On-premises Administration | |||
| Use the same domain for Lync on-premises and Lync Online users | No | No | No |
| Splitting workloads (for example, running IM/presence/voice on-premises, and conferencing in the cloud) | No | No | No |
| Windows PowerShell support | Yes | Yes | No |
| Web-based user interface (Lync Server Control Panel and Lync Online Control Panel) | Yes | Yes | No |
| Attendee/user reporting | No | No | No |
| Reporting (using CDR and Quality of Experience (QoE))) | Yes | No | No |
| Third-party API Support | |||
| Client automation APIs (client-side only) | Yes | Yes | No |
| Server side APIs | Yes | No | No |