There's no slang substitute without looking stupid. You could write 'wtchng' but I do not recommend unless you are on a pay-by-character plan.
Text You Back
gtk
make love to me
killing myself laughing
First, look up some slang, if you don't already know any. Most people know lots of slang. Second, imagine two people talking. Third, write down what you think they would say in slang.
welcome back (to a text or chatroom) or write back lyk tb text back
IZZY
. On My Way
Miss You!
penis
Text You Back
gtk
lpl
Did not laugh/does not like
Thanks In Advance
you take care :)
make love to me