SINGAPORE - A price war has erupted in the mobile space for the first time in four years, with telcos essentially halving prices depending on the mobile plan.

Telco M1 has followed Singtel's lead, and is now upsizing new and recontracting customers' mobile data allowance at a fixed additional cost of $5.90 a month.

On Thursday evening, StarHub also joined rivals, allowing customers to pay $3 more a month to add an extra 3GB of mobile data to their existing bundle. The promotional rate will last until the end of this month. From April, the add-on fee will be $6 a month.

This means StarHub's 6GB mobile plan now costs $45.90 a month, or half of what it used to cost customers.

Singtel yesterday announced its new add-on plan DataX2 that gives new and recontracting customers the option of doubling their mobile data allowance when they top up $5.90 extra a month.

M1's add-ons vary from 2GB to 12GB depending on the mobile plans.For instance, customers signing up for M1's basic $42 monthly plan that originally comes with 3GB of data allowance will get to add on 2GB. The package that comes with a total of 5GB of data will now cost $47.90. Before this, customers had to pay $82 a month for 5GB of mobile data. This works out to a discount of 40 per cent.

The biggest discounts are for higher-end plans. For instance, M1 customers now get to add on 6GB of data to their existing 7GB bundle. They pay only $107.90 a month for a total of 13GB of data. Its 13GB plan used to cost twice as much at $228 a month.

Similarly, Singtel's monthly $102.90 plan that originally comes with 6GB of data can be bumped up to 12GB for a total of $108.80. A 12GB plan used to cost twice as much at $239.90.

M1 has also bumped up the data allowance of all its line-only plans by at least 1GB if customers sign a 12-month contract. For instance, customers used to get 5GB of data for $30. But now they get 6GB of data.

The telco, which was the first to roll out line-only plans in July last year, also added two new low-end line-only plans offering 1GB and 4GB of data for $15 and $20, respectively. All its line-only plans come with at least 100 minutes of outgoing phone calls and 600 SMS/MMS.