I have the LG GT350 and every time I try to send a picture it says "not enough memory" when I have enough memory on my phone. I have umlimited texts so it can't be that I don't have enough credit :/
Have you tired adding a little extra memory using a memory card?
Personally I would consider a new phone because LG is rather.. Ironic? If that's the word? LG standing for 'Lifes Good' and having one of their products just makes life crap xD! Either way, you should try clear your unwanted text messages to clear a little space. That could help a little but as you state you do have enough memory. If you have tried several things already and still can't seem to send a picture then try getting in contact with LG.
Maybe you have too many texts saved in the outbox? Try clearing sent messages. If its not that then perhaps the phone has an electrical malfunction of some sort.