Of course you can surprise your (girl)friend by introducing sextalk when you phone. But if your lover has just caught a bus, your timing is off. If you want to combine it with masturbation you better set a time that you’ll call.
Get in the mood before you call, by fantasizing, thinking about what you are going to say, reading an erotic story or thinking about the last time you had sex.
If you are nervous, pretend your lover is on the phone and talk. Start masturbating and describe what you are doing. Discover which words you like to use and which turn you off. Don’t hold back the sounds that naturally emerge when you pleasure yourself. So practise at a time that you have the house to yourself.
What you tell your lover can be fantasy based. You can wear the most exciting outfits, while you are just naked or you can talk about things that don’t excite you, but are a known turn-on for your lover. But you can also talk about things you would like to do when having sex the next time.
If you are alone you can practise your voice. Make it sound sexy, without it sounding feigned or unnatural. You have to learn how to strike the right note.