It depends how u want to view this.
In my group of mates theres a 'thing' about eveyrone trying to be the first person to txt the birthday girl/boy at midnight, therefore everyone does it! But if in your group of well, so called 'mates' txting isn't such a big deal then dont make it one.
I still think they should have made some effort though. Maybe give them a call and let them know its upset you, and if they seem apologetic (genuinely) then it may not be sucha big deal, but if they dont give a flyin **** then they aint worth it at all. Friends should always want to wish eachother a happy birthday and buy each other presents etc, so find out why, u never know they could be planning you a surprise party..