how to delete my phone number from imessage

Does anyone know how to delete their phone number from imessage, yet still use their iphone and still leave imessage on, on that iphone? All options equate to either not using that phone anymore and/or turning imessage off, which do not apply to me. I have an iphone, and use it as my regular phone and phone number. I also use imessage a lot, but only through my email and with particular people who I need to imessage with due to restrictions with texting - ie. people who live in another country etc. However, if I turn on my imessage on my phone it automatically connects my phone number to imessage, I have no choice, and when you try to deselect it until settings-messages it is greyed out; this should be a choice for the user. The issue that happens is my contacts with iphones will message me, say when I'm meeting them and their phone auto selects imessage and then I'm wherever, meeting them, and not getting any messages because I'm not at home with wifi as I don't have, don't want and can't afford data, and this causes a lot of issues. I also can't ask my friends, nor are they going to remember to ensure they text me and not imessage me, and there doesn't, again, seem to be a choice there anyway....choices seem to be ever decreasing in the 'apple product world'. There doesn't seem to be an answer to my problem and it seems simple to me that this would be an issue for many, but I thought I'd ask around before giving up. If I deregister my number, once you turn your phone back on, it auto re-registers the number....Thank you!