Very strange... I've never heard the automated woman at new street.. do they still use her?
Birmingham New Street along with many other stations (mostly in southern England) use what is known as a Ditra to do the automated announcing (because it's made by Ditra Systems).
It is voiced by two people, a man (Phil Sayer, who is by far the best automated announcer I've come across), and a woman (Celia Drummond, who I find annoying to put it bluntly).
Some Ditras (particularly the older ones the Thameslink side of FCC have) are extremely basic and only have the necessary data loaded into it for the station it is used (which reminds me - almost 5 months on and Luton's still cannot say 'East Midlands Trains' :roll

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Others, such as those operated and owned by SWT and Southern, are incredibly sophisticated and (I believe at least) the SWT Ditras have every file loaded into them. They are so sophisticated they can announce LU engineering work, tell you the next train from a platform if one is delayed/cancelled, and even tell drivers of a specified road vehicle to move it if it's in the way.
Also several factors lead me to believe that SWT Ditras are placed at strategic network locations and are operated remotely via long line PA (e.g. announcements at unstaffed stations).
It is my understanding that on the non-basic ones (which I think New Street's comes into) have both Phil's and Celia's voice in them and all it takes is a simple changing of the admin settings on the system to change who does the announcements.
In the case of New Street I think they regularly test out Celia (maybe they get bored...) and test public response to her.
Many stations use the two voices together on alternate platforms so that people can distinguish which announcement is for which platform and SWT also has a habit of switching them every couple of months 'so customers don't switch off to the same voice each day'. Celia's voice is also used on the SWT Desiros after replacing Phil's towards the end of 2006/start of 2007 and also on the 455s. CIS improvements are also due on the Sprinters this year.