I found a firmware for Spark devices which can be widely adapted. They seam to have a lot ppp software packages on the feed to download and install with PB expert menu. Maybe you could try if you can get 3G-UMTS running with this image or to get kernel and modules from it and put it into a HDMU image. Latest image I found is releaseS-spark-20140512.zip.

nigma2:
Machine: spark
Date: 20140512
Issuer: pbnigma
http://www.pb-powerboard.com