I am emailing or texting mine at a regular intervals with great success. When I do a job I decide that day when I will contact the client again. This could be anything from 1 day to 2 years in the future depending on the opportunities available. This is logged on my computer system and every day my computer system prompts me with a small list of people whose reminder time is today.
I treat it as a simple reminder and do not follow up again until 3 to 6 months later, if I do not get a response.
Look upon it as providing a good service but make sure that you don't overstep the mark. I email or txt something along the lines of :-
Dear ..........
Happy New Year. I hope that you and the family are well.
I notice from our records that it was September 2008 when we gave the apartment carpets a full clean. This is just a courtesy email to see if you feel the carpets are ready for sprucing up in the near future. Let me know if you need an appointment..........
My diary is pretty much full for the next 5 weeks which I put down to the success of this system.
You have nothing to lose and lots to gain.
Good luck
Nigel
www.designcare.co.uk