DON'T DO IT!! Unless you want all your text messages to be erased, even locked messages. I did it today in desperation to end this GD Low on Space crap. My Dialer Storage was over 43MGs and did not realize it erased the text messages. I thought, being it is titled "Dialer Storage", not Text Message Storage, that it would not erase them. I lost some important texts about money and work hours. FAAARG!
My suggestion is to go into your messages, lock all the ones you want and erase all unimportant threads or message. I know it takes a poop load of time, but if you want to save certain messages, Do Not Erase the Dialer Storage Data.
Best of luck.
FYI-I had been receiving the low on memory for the passed 8 months, then final had it. There was SOOOO much available memory on my phone, yet the 44MGs in the messages was causing this??? B to the MFn S, HTC. But the warning is gone now, along with valuable messages. Grrrrrr.