lucky you...i preordered on sept, 10, 2009 and still did not get mine! 
as for the mic issue, it seems that it may be stuck on mute.
try to find the settings by going through the menus (if i had one, i would know more, maybe someone else can help you better on that part) and check to be sure that you are open to use on your settings and not muted.
if that doesnt work, try to see what happens after a reboot, which you probably already tried.
if that doesnt work, try to reformat the unit,
if that doesnt work, try to completely reinstall the OS
and...if all that fails, send it back! i would try all the above first, because regardless of the time to try it all, it is going to be much longer when you send it it and expect a return.
is this something that has recently happened or has this always been the case with your phone?
Some people have reported the microphone on the handset does not work on their handsets. They have either returned their phones for a refund or a replacement. In some cases this has been a lengthy (and ongoing) process I'm afraid
If, however, your handset HAS worked since you first received it, then it could be a mute problem.. It is worth looking for the recorder package to test the microphone..
If your microphone has always been silent, you may have a dud I'm afraid.. bad luck there 
My first impressions:
picked up from the flagship store in regent st on Sumday and had to take the kids shopping for pressies so couldnd play with it for a good few hours until i got back home.... very frustrating .) i did take a peak and was suprised at how small the phone looks 'in the flesh' keyboard is nice and compact but could pose probs for people with fat fingers.
if you place on top of an iphone its almost exactly the same size. just a lot thicker.
screen is stunning when you spark it up for the first time and the browser blows any device of this class out of the waterby a wide margin. im writimg this review on my device whilst in bed .) excuse any typos....
i did a lot of research before parting with my money and there was a lot of internet chat about battery life. the first two charge cycles gave me resonable performance and now i can easily get a day of pretty heavy use from 8am until 1900.. wont go into my usage but battery aint an issue for a device of this class and as we are only on public firmware release 1 it can only get better.
after the excitement of powering on subsided i felt a bit dissapointed' especially seeing it cost me 500 quid. this lasted a day. it takes a bit of getting used to the interface and then it all starts to come together. yes there are a few interface issues that need sorting. my main gripe at he mo is currently no mail4exchange support for 2k3 but that can be sorted and the maemo boys are looking into it.
compared to previous handset releases this one seems to have gone very well if you take into account this is the first maemo device that nokia have released that is also a phone.i like to call it a hybrid 
i can now say im loving it and my netbook is now gathering dust. i can browse the internet whist watching tv with the wife and its just as good as a netbook but a lot more portable!!
camera up to normal nokia high standards geotagging works well for me. very fast plus like the tagging of images for searching large albums. im also loving the customisation possibilities of the whole desktop. once i got the hang of the phone i spent 6 hrs adding and moving stuff about so everything i use daily is a click away.
once mfe is running contact calandar sync will be good. done an initial sync through the suite and the calandar\contacts diisplay is first class. possibly due to the nice screen res. it all fits on nicely and the calandar month view is so much better than on my bb. looks similar to outlook
x terminal aint too bad for the more advanced users. i set font to green with black background for a nice retro look. much better than the default! font size can also be reduced due to the nice screen so u can see a lot more text and its still clear
reckon in the next few days ill have more to say but the device defiately grows on you the more you discover..
