The default dial plan on Polycom handsets does not allow dialing 3 digit extensions starting with 10. Typically you would notice this when trying to transfer a call and you get a voice prompt along the lines of "that extension number is not valid".
To resolve this, log into the handset web-interface, browse to the 'SIP' options page, and remove all settings related to 'Digit Map'.
Typically, the default digitmap settings are:
DigitMap: [2-9]11|0T|011xxx.T|[0-1][2-9]xxxxxxxxx|[2-9]xxxxxxxxx|[2-9]xxxT
DigitMap Timeout: 3|3|3|3|3|3