There are probably better ways, but this seems to give something like what you look for:
\starttext
\setupTABLE[c][align=middle]
\setupTABLE[c][odd][width=2em]
\setupTABLE[c][even][width=1mm]
\setupTABLE[r][2][height=1mm]
\setupTABLE[c][1][leftframe=off]
\setupTABLE[c][5][rightframe=off]
\bTABLE
\bTR
\bTD 1 \eTD \bTD \eTD \bTD 2 \eTD \bTD \eTD \bTD 3 \eTD
\eTR
\bTR
\bTD \eTD \bTD \eTD \bTD \eTD \bTD \eTD \bTD \eTD
\eTR
\bTR
\bTD 4 \eTD \bTD \eTD \bTD 5 \eTD \bTD \eTD \bTD 6 \eTD
\eTR
\bTR
\bTD 7 \eTD \bTD \eTD \bTD 8 \eTD \bTD \eTD \bTD 9 \eTD
\eTR
\eTABLE
\stoptext