FYI there's a topic in the "Android Phones" area for your phone. You might get better results there.
Are you trying to add to your primary memory (where program images live while they're executing) by mounting a partition on your external SD card? I don't think that will work. You're not going to see more system RAM that way.
If you're out of system RAM, you can add virtual memory in the form of a swap partition (ID 0x82), and using swapon or even better, adding an entry to /etc/fstab so it "mounts" automatically. Using slower secondary storage will not be as fast as adding more system RAM, but it's probably your only choice, since I haven't seen any smart phones with SODIMM sockets that would allow a "bigger" RAM card to be added.