Afraid not.

The two best options:

a: a couple of $10 prepaid calling cards.

b: get an "800" number that's associated to
the cellphone. (It can be 800, 888, 877, 866).

One vendor is Kall8, which charges a fee
of about $5 month for overhead, then 10
or so cents/minute. (I may be off a bit on
those rates, but while they're not the
absolute best, they're reasonable).

The beauty of Kall8 is that they have
a very well designed web-page control
system, which you can use to set up the
tollfree number with all sorts of options,
the key ones being

    a: where it goes to
    b: and where it takes calls from

with "a", you can route the calls to go
to your cellular phone, or to your landline,
or your office, or your nephew's landline
when you're visiting. Changes take place
just about instantly.

with "b", you can block any calls from
the 49 states you don't expect people to
be calling you from, so you won't waste
time or money with wrong numbers.

(You can fine tune the various settings).

http://www.kall8.com

disclosure: I'm a customer. No other connection.

What I would do is to get him an account at OneSuite, which has a toll
free access number (it costs 2.9¢ per minute, a bit more per than the
2.5¢ per minute for local access numbers), plus 55¢ for toll-free access
from a pay phone (if he has to call from a pay phone).

This would be a much, much cheaper option than calling collect, and he
isn't tied to calling only his parents (which he would be if they got a
toll free number forwarded to their cell phone). The parents can add
money to the account as needed.

"http://www.onesuite.com/default.asp"

OneSuite is usable from a lot of countries (Australia, Austria, Belgium,
Canada, China, Denmark, France, Germany, Hong Kong, Hungary, India,
Ireland, Israel, Italy, Japan, Korea, Luxembourg, Mexico, New Zealand,
Norway, Spain, Sweden, Switzerland, Taiwan, U.K.), with toll-free
numbers in each country. It's the only calling-card like service I know
of that has access numbers both inside and outside the U.S.. If your
grandson is stationed in one of these places then it'd be really useful
to have a service that works like this.

Once he calls, it'd be cheaper if the parents call him back using
OneSuite (if the phone he's calling from accepts incoming calls),
because the rates from the U.S. to other countries are cheaper than the
rates from other countries to the U.S..

I have a similar issue with a relative who lives in a gated community
where they can only make collect calls. Unfortunately the management
association doesn't allow the residents to make calls to toll-free
numbers, they can only call collect.