Wait a minute.
What other base stations?
The handset listens to the paging channel of only one station.
And it is the current base station selected as discussed earlier.
Again from the same book:
Yes, the handset (MS) maintains a preferred base station for the purposes of two specific things: 1) listening to the PCH (the paging channel, on which the network broadcasts to the handset that it has an incoming voice or data traffic request); 2) where to send a RACH request (RACH is an acronym for "Random Access CHannel", and it's used by the handset to send a request to the network for outgoing voice or data traffic, and to request a dedicated traffic channel for this traffic.
So, for the sake of the discussion, let's assume that the handset performs a search for base stations from which it can receive a signal, and that it identifies five different base stations (A, B, C, D, E). Let's then assume that the handset selects base station A as the station whose PCH it will listen for, and whose RACH it will page if it wants to make an outgoing voice/message transmission.
But when the handset receives an incoming voice or message alert via the PCH from base station A, it does not then have to use that particular base station for the voice/data transmission. And in the case of SMS or MMS, many GSM networks instruct the handset to use one of the other base stations which are also within signal range, if the traffic channels on the base station from which the PCH alert was reached are almost full.
So in this example, if the traffic channels on base station A were fairly congested, the network would instruct the handset to perform an RACH handshake with, say, base station D, which might have light transmission traffic at the time. In this way, the network can balance traffic and ease network congestion.
Similarly, if the handset sends an RACH page to request a channel for voice or data (i.e. the mobile user wants to make an outgoing call or send a message), it would send it to base station A. But base station A can respond to say that its traffic channels are getting full up, and that the handset should therefore try sending an RACH request to (say) base station C.
For both the situations outlined above, the network is far more likely to redistribute SMS/MMS traffic than voice traffic. This is because SMS/MMS traffic is relatively very short in duration, but occupies an entire traffic channel* for the period of transmission. It therefore makes sense to "fit in" SMS/MMS traffic around small gaps of inactivity on the traffic channels, in between voice calls (which use the full channel for the entire duration of the call). Therefore, it's far from unusual for a handset to receive (and send) SMS messages from a base station which is not the one with which it has established a PCH/RACH connection.
When I was writing about the handset listening to multiple base stations, I was being colloquial, since I didn't want to get involved in describing the full handshake procedure over the various channels. The more detailed picture is that the handset retains an ongoing communication with just one base station, but that as soon as an incoming alert is received over that base station's PCH (or an outgoing request is sent over the RACH), the other base stations within signal range also potentially come back into play.
Sorry to get complicated and a bit technical, but it seemed necessary in order to explain more fully how it all works in practice.
* although most networks can now squeeze SMS onto half a channel through a further CDMA algorithm.