There's another version of XHTML, which is also in recommendation status: XHTML Basic. XHTML Basic is a very small subset of XHTML, reduced to the bare minimum so that it can be supported by devices considerably simpler than standard PCs. You can find the XHTML Basic recommendation at www.w3.org/TR/xhtml-basic.
If you want to use XML Basic, here's the <!DOCTYPE> element you should use:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">