Question: Texting from cellphone versus emailing from cellphone

Folks,

If you wanted to send an email to somebody from your cellphone or send
a text message to that person's phone number from your cell phone, what
would you prefer(from a cost perspective)?

In other words, Is it any cheaper to send a "message" to a phone number
(called SMS in Europe/Asia and 'Text message' in North America) or to
compose an email to the receipent from your cell phone?

Assume that the recipient doesn't care either way. My question is what
method *you* would choose, especially if you want the cheapest option?

For example, in my cell phone (for Tmobile service provider, USA), when
I select "Send a message", my phone prompts me for an address book
entry to send the message to. It
doesn't care whether I choose a phone number or an email address. My
service provider too charges the same price for every outgoing message,
regardless of whether it is a text msg or email.

I am thinking (hoping, rather) that they will cost the same for most
people too, just as it is for me. In any case, any answers will be very
deeply appreciated.

Thanks!
ash