RewriteEngine on

RewriteCond %{HTTP_USER_AGENT} "DoCoMo" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "J-PHONE" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "Vodafone" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "SoftBank" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "KDDI" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "UP.Browser" [NC]
RewriteRule ^$ http://www.abc.com/i/ [L]

ここまで調べました。
一番最後の行の
RewriteRule ^$ http://www.abc.com/i/ [L]
これは、URL表示が
http://www.abc.com/i/
ってことですよね?