Yes -- you can knit the band right along with your sweater. For instance, if the sweater is in stockinette, you can switch to garter for the five or six stitches for the width of the bands. Takes some planning to make your buttonholes right.
Or, you could knit the entire cardigan without the bands, then pick up the stitches and knit the bands right to the cardigan -- no sewing. If you do it this way, I would suggest you avoid ribbed bands, even though some patterns call for them -- I've found they sag when used this way. Garter is good, and so is seed stitch. Use a smaller needle than you did for the cardigan.