How can I do a factory reset on a MyTouch 3G Slide?
To do a factory reset, you should be able to go to Settings -&gt; Privacy and hit Factory data reset.

Alternatively though, to just clear the SMS data you should go to Settings -&gt; Applications -&gt; Manage applications and find the SMS app ("Messaging" or similar) and clear the data for it.  There may also be something like "Messaging Storage" that you need to clear.

If you really need to boot into recovery, I would try the following:


Hold power and volume down until the phone reboots or turns on
Hold the power button for two more seconds, then release it (if the phone reboots again, you held it too long)
Keep holding volume down until recovery mode appears