Assuming you are using the Generic Phone, edit the following file :

C:\Program Files\Macromedia\Flash 8\en\Configuration\Mobile\Devices\Generic_Phone.xml

and change the line

<device id="8502" width="176" height="208" heap="1024">

to

<device id="8502" width="176" height="208" heap="2048">

Increase the heap value as necessary.