The following articles include detailed guidance and formulas for calculating acceptable bandwidth consumption estimations for various scenarios in Citrix XenApp and XenDesktop. Each user in XenApp and XenDesktop is modelled and organized into various user types, such as heavy HD video streaming or Autocad application worker or lightweight Internet browsing and office application worker. Printing also is a major factor which contributes to bandwidth consumption in XenDesktop user sessions.
The following article (https://support.citrix.com/article/CTX133024) provides a very good analysis of softphone/VoIP integration with XenApp and XenDesktop. If the softphone installed in XenApp and XenDesktop does not belong to one of the major supported vendors (Cisco, Avaya, Vodyo), then the soft phone application should be running under the generic SIP over ICA configuration category. The various client-server software packages, such as the Citrix Realtime Optimization Pack for Skype for Business server optimize the end user experience. However additional Citrix technologies, such as the Adaptive Transport and EDT protocol help optimize the end user experience in terms of bandwidth and latency management.
When considering thin clients for XenApp and XenDesktop environments, the major consideration and decision point should be to determine if the thin clients are certified by the Citrix Ready program: https://citrixready.citrix.com/. Citrix recently released the “Workspace Hub” initiative which offers Citrix-ready thin clients supporting HDX RealTime Optimization Pack at low cost. Citrix works closely with Stratodesk and their NoTouch OS Desktop in order to provide old PC re-purposing and thin client utilization capabilities to customers.