how to contac quick without number or facebook?

[melissa]

so im meeting up with a friend at the trafford center 2 day in H&M but i said i would be there 4 1pm im not going to be able to make it till 2pm though she isnt on fb and i dont know her number but she knows mine how do i tell her that im going to be late
(she isnt on fb at the mo but she is on her phone ?
help plz
sorry thanx 4 the answer but i have a crappy phone so it has to be something real simple thanx