Why not just text him really random and obnoxious shite at early hours of the morning.

''Want to be debt free in 597975 years? Call FirstPlus now!'' or ''Take our new enlargement drug, can add 2'' to your penis if taken 64 times a day for 2 weeks''

That's more annoying than fuck off. Sign them up for some horoscopes and darts/fishing/curling championship news bulletins too....they always cost over the odds and tell you nothing of worth. Few crazy frog ringtones at £5 a shot should annoy him prefusely aswell.