I called the upgrade centre to order an Ericsson T39m. This would, effectively, be a free upgrade as the price of the 'phone was less than the voucher value. Unfortunately it was out of stock and I was asked to call back in a couple of weeks time. One thing led to another and a month had gone by.
When I called yesterday I was told that the T39m was now free. As was a number of other 'phones. So, I've ordered a Nokia 8310 and I get to keep all my Equity points.
I was surprised that the 8310 was free; under the original offer it was 149.99gbp.