you can download idialer, then map your phone softkey to open up idialer (or any other dialer for that matter):
Change Left or Right Softkeys in Manila
HKLM\SOFTWARE\HTC\Manila
For Right Softkey (for example, setting it to Comm Manager):
"HomeRSKText"="Comm Mgr"
"HomeRSKPath"=\Windows\CommManager.exe
For Left Softkey (for example, setting it to All Contacts)"
"HomeLSKText"="All Contacts"
Taken from here: http://forum.ppcgeeks.com/showthread.php?t=110249