syncme.sebeta performs synchronization of Google Calendar with SyncML supporting cellphones in a manner that easily outperforms all other alternatives.
Opera Mini and this kind of calendar synchronization enable me to use my now over three years old Sony Ericsson s500i much like it were a modern smartphone. I realize the phone is as ubiquitous these days as the Nokia 3310 was in the early 2000s, but I take comfort in being a pioneer: I got the phone about one to two months after it came out.
But none of that is really relevant. If you use Google Calendar and a phone that supports SyncML, syncme.se might just be what you were looking for.