It is perfectly acceptable, i know an invitation i got recently had thr address, email and mobile number to text. We live in sucha fast world, and also people living coutries apart it makes things so much easier. also includedin my invites a postcard with asecond class stamp on, with the adress pre written on so all they had to tick was yes or no, and then a number, and had a space on their for special dietry requirements.