Is it true that the Bible says only 144,000 people will be allowed into heaven? Are my Jehovah's Witnesses friends right?

The misunderstanding is based on an over-literal reading. If we took the number literally, which in a book like Revelation would be highly unwise--opposite the normal rule of interpretation in non-poetic, non-"apocalyptic" literature--then we would be obligated to take every element of the passage literally. Look closely at Revelation 7:4 and 14:1-5.

And I heard the number of those who were sealed, one hundred forty-four thousand, sealed out of every tribe of the people of Israel (7:4).

Then I looked, and there was the Lamb, standing on Mount Zion! And with him were one hundred forty-four thousand who had his name and his Father's name written on their foreheads... It is these who have not defiled themselves with women, for they are virgins; these follow the Lamb wherever he goes. They have been redeemed from humankind as first fruits for God and the Lamb, and in their mouth no lie was found; they are blameless (14:1, 4-5).

Clearly this is a symbolic number. Of course, you and I know that this is a symbolic passage. 144,000 = 12 (the number of organized religion) squared, x 10 to the 3rd (10, the number of man raised to the 3rd power, the power of the divine number). Women will be in heaven, not just men. And so forth...

Revelation is full of numerical and other symbols, which are common characteristics of this genre of literature, called "apocalyptic." If your Jehovah's Witness friend wants to press the details of Revelation 7 and 14 literally, you can refute him by (tongue-in-cheek) insisting that:

* Only Jews go to heaven.
* No females are allowed.
* No Jews from the tribe of Dan will be there.
* No one who has experienced sexual intercourse is welcome.

We see that the redeemed are (1) Jews only, though not from the tribe of Dan, (2) males only, (3) virgins only. In other words, unless you are a celibate Jewish male (not descended from Dan), you have no hope of heaven. I am quite sure my female readers would disapprove of such an interpretation, but 99% of my male readers would also reject the literalistic understanding.

For more on this, may I suggest you read Gordon Ferguson's Mine Eyes Have Seen the Glory (Woburn, Mass.: DPI, 1996), Jim McGuiggan's Revelation (Fort Worth: Star, 1976); or my audio set Revelation and the End of the World (IPI, 2005).