Hi Stewart,
At BT, we are constantly working to improve the quality of service for our customers and this includes the development of firmware upgrades, which undergo vigorous testing before they are launched. 5.29.117.6 is the current version of firmware and unfortunately we have no announcements to make at this time. All upgrades will be made available to customers simultaneously as part of an automated process.
Broadband Voice works with the majority of analogue handsets, so you should find that changing your telephone will solve the issue.
Could you further describe the brand/model of your phone to help us improve our support?