If your friend with a Nextel phone has the NextMail service add-on ($7.50/mo), then your friend can set you up as a "NextMail Buddy" in their online NextMail account, then you can freely send texts from a PC to a Nextel phone at no additional per-message cost. The Nextel phone user answers with the PTT button, so you will not receive a text message back, you will receive an MP3 voice recording of their message.
The PC has to be connected to the internet of course, because it is a web-browser interface into NextMail.
BTW, the SMS messaging system used for NextMail is fast, usually no more than a 15 second delay going either way.
Also BTW, NextMail is now also available for Sprint customers, no longer just for Nextel customers.
I don't know if it would be worth it to your friend to pay the $7.50/mo charge for NextMail, but it is an option if you are seriously needing reliable text messaging from a PC to your friend's Nextel phone. Because NextMail is an add-on, it can be added to any line within your friend's Nextel account, and dropped any time without changing the phone plan, i.e. it won't affect your contract date at all. Of course, if you add it, you have to keep it for a minimum of one month, you can't add it for just a day or two then drop it. Well, you can, but you'll pay for the whole month.
I've used NextMail since about 2005, so if you have any questions post them here (might be a day or two before I respond).
This generates an error message:
Mail System Error - Returned Mail
"Mail Administrator" <Postmaster@messaging.nextel.com> [Add]
Fri, 15 Oct 2010 2:09 PM (< 1 min ago)
Show full header
This Message was undeliverable due to the following reason:
The following destination addresses were unknown (please check the
addresses and re-mail the message):
<+[[my friend's number]]/TYPE=PLMN@messaging.nextel.com>
Please reply to <Postmaster@messaging.nextel.com>
if you feel this message to be in error.
Message was edited by: Alvin1947
I checked with the Product Manager for SMS on the iDEN network and she confirmed that the address is correct. She also sent a couple of test messages through Outlook and they all arrived. Are you certain your friend's phone is a Nextel phone? Is it possible, his provider is Boost? In this case you'd have to use @myboostmobile.com.