Since SMS has a hard limit, and is not going to change, are you sure you know about that limit?
That is, it's not a limit imposed by the phone.
I've recently bought LG Wink III C199 and I am having issues with sending long sms. The default maximum setting for sms sending is 4 parts (160 characters per part). If the sms exceeded 4 parts or 640 characters it will automatically be converted to MMS which obviously I'm trying to avoid. I'm subscribed to unlimited sms so once my messages convert to MMS, I will be charged with MMS rates. I usually send long sms daily for my work. I just want to know if there is a way to solve this problem internally (phone settings) or externally (using 3rd party apps). Appreciate your thoughts!